KEW BULLETIN VOL. 66: 425–439 (2011) The genus Isoglossa (Acanthaceae) in west Africa Iain Darbyshire1, Laura Pearce1 & Hannah Banks1 Summary. The genus Isoglossa Oerst. (Acanthaceae) is revised in west Africa, with particular emphasis upon the Cameroon Highlands. Four species are recognised, including Isoglossa dispersa I. Darbysh. & L. J. Pearce newly described here, and a second new species for which further flowering material is required before description, here called Isoglossa sp. A. Lectotypes are chosen for I. glandulifera Lindau and I. nervosa C. B. Clarke and the status of the latter species in relation to the eastern African I. membranacea C. B. Clarke is discussed. The habitat, ecology and conservation status of each species are considered, and gregarious mass-flowering is reported in I. dispersa. Key Words. Cameroon Highlands, conservation, dichotoma complex, glandular hairs, plietesial, pollen, taxonomy. Introduction The genus Isoglossa Oerst. (Acanthaceae: Justicieae: Isoglossinae sensu Kiel et al. 2006) comprises approximately 50 – 70 species in the palaeotropics. It is most diverse in east Africa, where recent revisionary work for the Flora of Tropical East Africa recognises 30 species (Darbyshire 2009). In west Africa, only two species were enumerated in the Flora of West Tropical Africa account: I. glandulifera Lindau and I. nervosa C. B. Clarke (Heine 1963). However, three further “imperfectly known species” were listed, based upon single collections of doubtful position. Since the publication of that account, numerous further collections of Isoglossa from the Cameroon Highlands (sensu Cheek 2004) have accumulated in herbaria and it has become apparent that (a) more than two species are present, (b) the two existing names have frequently been misapplied on herbarium material, and (c) the west African taxa have not been compared in sufficient detail to closely related east African species. This paper therefore presents a revision of the genus in west and west-central Africa. Several species of Isoglossa are known to have a plietesial life-cycle, ie. perennial monocarpy with gregarious growth and mass-flowering over a cycle of years (see Darbyshire 2009). Mass-flowering events have been recorded in two species of Isoglossa by Thomas (1996), who listed these as probably I. glandulifera and I. nervosa. Recent field observations confirm that I. dispersa, newly described here, is a gregarious mass-flowerer at least in Guinée (see Fig. 4B); at Mt Béro an estimated two million plants were recorded in nine subpopulations over c. 3 ha in January 2011 (P. K. Haba, pers. comm.). Further field surveys are proposed for these populations to determine whether flowering is on an annual basis or whether they are true plietesials. It is worth noting that this species was not recorded during a rapid botanical survey of Mt Béro in November 2008 which may support the theory that this is a plietesial species. Materials & Methods Herbarium material of Isoglossa from west and westcentral Africa held at B, BM, BR, EA, HBG, K, P and YA was studied at K together with additional material digitised by the Aluka African Plants Initiative (www. aluka.org). Floral dissections of herbarium material were made following soaking in Aerosol OT 10% solution. Photographs of Isoglossa flowers were studied where available to assist in the description of flower shape and colour. For study of the pollen, an anther was extracted from a flower bud on a representative herbarium sheet of each species, dissected to extract the pollen, and mounted onto a SEM stub coated with double-sided sticky tape. Seeds were also mounted onto SEM stubs using double-sided sticky tape. These preparations were then sputter coated with platinum and examined using a Hitachi S4700 cold field emission SEM at 2 kV. The categories and criteria of IUCN (2001) are applied in the conservation assessments for each taxon; Area of Occupancy (further AOO) was calculated based upon an average population size of 4 km2 per locality, this being the recommended cell size following the IUCN Standards and Petitions Working Group (2008: 33). Species affinities in west African Isoglossa The circumscription of the genus Isoglossa has been discussed in some detail in previous works (see Accepted for publication September 2011. 1 Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK. e-mail: i.darbyshire@rbgkew.org.uk © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 426 Hansen 1985; Kiel et al. 2006; Darbyshire 2009). Briefly, it can be recognised by having the combination of a subregular 5-lobed calyx, a two-lipped corolla, two bithecous stamens, the thecae often offset and always basally muticous, an absence of staminodes and a four-ovulate ovary, the placenta not rising elastically at capsule dehiscence. Further, most species of Isoglossa have “gürtelpollen”, i.e. biporate pollen, circular in polar view and with a more or less pronounced marginal girdle (Lindau 1895); this is the pollen type recorded in all the west African species (Fig. 1). The four West African species of Isoglossa recognised here fall within the I. dichotoma (Hassk.) Hansen complex in which the species share a laxly paniculate compound inflorescence (thyrse), small white, pink or purple corollas and strongly offset anther thecae (see Darbyshire 2009). This group accounts for much of the diversity in east Africa, where most of the species are recorded from montane and submontane forest and often have a highly restricted range (Darbyshire 2009). The west African species are also mainly forest dwellers, although over a wider altitudinal range and KEW BULLETIN VOL. 66(3) extend into grassland above the upper forest margin in montane regions. Developmental variation in inflorescence indumentum Poriazis & Balkwill (2008) studied the developmental variation of a monocarpic species of Isoglossa (their “Isoglossa sp. 1”) from South Africa over a growth season and found changes in inflorescence indumentum with maturity. The bracts on the young spikes were eglandular-ciliate only, whilst at fruiting they were also glandular-viscid. They postulated that the increase in viscidity may be in order to protect the fruits against predation. Similar variation can be inferred from herbarium material for several east African species of Isoglossa. For example, in I. ventricosa I. Darbysh. from south Tanzania, the most mature specimen seen to date (Congdon 175 ( EA, K)) has densely glandular pilose inflorescences, whilst specimens with immature inflorescences (e.g. Lovett 2257 (DSM, K, MO)) are eglandular-hairy only (Darbyshire 2009). Fig. 1. Pollen SEM images of west African Isoglossa species: A I. glandulifera (Boughey 180); B I. nervosa (Jacques-Felix 9092); C I. dispersa (Letouzey 13201); D I. sp. A (Hepper 4110); all scale bars = 10 μm. © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 427 THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA Similar trends are also found within the west African species. Of particular note is the newly described Isoglossa dispersa I. Darbysh. & L. J. Pearce. Here, the distinctive ellipsoid (sub)sessile glands, which give the inflorescence a papillose appearance (Fig. 5B & C), appear only to develop at maturity. On Letouzey 13201, in which the inflorescences are young with only the first few flowers emerging, the glands are sparse and not fully developed, whereas in mature fruiting specimens such as Lightbody in FHI 26290 the glands are very dense. Mature flowering specimens are intermediate. An increase in the number of glandular hairs with maturity is also evident in I. glandulifera and I. nervosa. Therefore, whilst inflorescence indumentum is a useful character in the separation of the west African species, it is only applicable when mature inflorescences are available. Taxonomic Account The west African species of Isoglossa are easily separable by application of the key below. In addition, fruiting material is separable by close examination of the seeds which differ in type, length and ornamentation of the tubercles. However, these differences are difficult to convey in a key and it is best to compare the seeds to the SEM images presented in Fig. 2. The seed ornamentation is visible under a × 10 hand lens, though higher magnification is preferable. Key to species of Isoglossa in west and west-central Africa 1. Cauline leaves with base cordate or rounded; inflorescence with conspicuous patent glandular hairs 0.5 – 1.5 mm long only, lacking eglandular-puberulous hairs; corolla tube slender, ± cylindrical in the lower half and only slightly widened towards the mouth, 10.5 – 16 mm long, longer than the lower lip (Fig. 3P) . . . . . . . . . 1. I. glandulifera Cauline leaves with base attenuate or cuneate; inflorescence either with sessile or short-stalked glands to 0.2 mm long (then usually also eglandular-puberulous) or if with longer glandular hairs then always also eglandularpuberulous; corolla tube campanulate or if subcylindrical then much shorter, 3 – 8.5 mm long, shorter than or equal to the lower lip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Capsule puberulous, also with scattered short-stalked glands and/or long eglandular hairs; corolla shortly pubescent externally at least dorsally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. I. nervosa Capsule glabrous; corolla glabrous externally except sometimes for a few hairs along the lobe margins . . . . 3 3. Mature leaves very large, over 15 cm long; stems glabrous; mature inflorescence with numerous (sub)sessile ellipsoid glands appearing papillose (Fig. 5B & C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. I. dispersa Mature leaves much smaller, less than 10 cm long; stems antrorse- and/or retrorse-puberulous on paired opposite ridges; inflorescence with short-stalked capitate glands . . . . . . . . . . . . . . . . . . . . . . . . . . 4. I. sp. A 1. Isoglossa glandulifera Lindau (1894: 54); Lindau (1895: 229); Clarke (1900: 229); Heine (1963: 424); Lebrun & Stork (1997: 484); Vollesen (1998: 3), pro parte excl. Cheek 5355; Vollesen & Ghogue (2000: 112); Vollesen & Darbyshire (2004: 226). Types: Cameroon, Buea, Preuss 746 (syntype B†) & near Mimbia, Preuss 1062 (syntype B†; lectotype K!, selected here). Slender perennial herb, decumbent, scrambling or erect, 20 – 120 (– 300) cm tall, lower portion of stems trailing and rooting at the nodes. Stems sulcate when young, subterete with age, glabrous or uppermost internodes glandular-pilose. Leaves somewhat anisophyllous or pairs equal; blade (excluding uppermost pairs) ovate or elliptic, 2.8 – 10 × 1.9 – 5.5 cm, base cordate or rounded, sometimes somewhat oblique, apex acuminate or attenuate, with short antrorse hairs along the margin and usually also on the main veins above, more rarely on the veins beneath, usually with few to numerous multicellular hairs between the veins above, appearing deflated in dried material, rarely (Luke 11807) with numerous short fine hairs above; lateral veins 5 – 7 pairs; petiole 0.6 – 5.8 cm long, glabrous or with few hairs on the ridges above; uppermost pair(s) of leaves reduced, sessile or shortly petiolate and with a cordate base. Inflorescence terminal, a lax panicle, pyramidal to oblong in outline, (3 –) 6 – 30 × 2 – 15 cm, few- to many-branched at maturity, branching along main axis opposite or often partially 1-sided or alternate, cymules sometimes partially secund; axes with sparse to numerous conspicuous patent glandular hairs 0.5 – 1.5 mm, gland tip capitate, main axis often glabrous in lower portion; main axis bracts oblong or lanceolate, 1.5 – 3 × 0.7 – 1.3 mm, apex often obtuse or rounded in the lower portion, becoming acute upwards; lowermost pairs of bracts often obovate, to 4 × 2.5 mm, or rarely foliaceous and ovate; bracteoles as bracts but 0.5 – 2 mm long, apex usually acute; flowers sessile or pedicels to 1.5 mm long, extending to 4 mm in fruit. Calyx lobes subulate, 1 – 2.5 mm long in flower, extending to 1.5 – 3.2 mm in fruit, with glandular hairs in the distal half or © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 428 KEW BULLETIN VOL. 66(3) Fig. 2. Seed SEM images of west African Isoglossa species, with detail of sculpturing: A & B I. glandulifera (Hepper 2172); C & D I. nervosa (Thomas 2626); E & F I. dispersa (Lightbody in FHI 26290); G & H I. sp. A (Letouzey 13152). Scale bars: whole seeds = 1 mm; B = 500 μm; D & F = 100 μm; H = 300 μm. © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA 429 Fig. 3. Isoglossa nervosa (A – K). A habit; B detail of base of lower leaf; C detail of indumentum of calyx lobe; D indumentum of minor inflorescence branch, variant with short glandular hairs; E flower, lateral view; F dissected corolla with stamen and pistil; G detail of apex of upper corolla lip; H anthers; J capsule with immature seeds; K mature seed. A – C & E from Cheek 5355, D from Jacques-Felix 9092, F – H from Mann 2009, J & K from Thomas 2626. Isoglossa glandulifera (L – U). L habit; M detail of base of lower leaf; N indumentum of minor inflorescence branch; P flower, lateral view; Q dissected corolla with stamen and pistil; R detail of apex of upper corolla lip; S anthers; T capsule with immature seeds, calyx persistent; U mature seed. L – P from Thomas 9170, Q – S from Cable 1397, T from Morton K839, U from Hepper 2172. DRAWN BY ANDREW BROWN. © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 430 glabrous. Corolla (16 –) 18 – 25.5 (– 29) mm long, white, pink or purple, with pink, red or purple markings on palate of lower lip and throat; glabrous externally, ventral portion of tube pubescent internally; tube slender, slightly curved at least when immature, 10.5 – 16 mm long, ± cylindrical in the proximal half where 1.3 – 3 mm wide, ventral portion gradually declinate in distal half, 3.3 – 5 mm wide at mouth; upper lip broadly triangular, 3 – 7 mm long, lobes held erect, 0.8 – 1.7 mm long; lower lip protruding, (5.7 –) 7 – 11 (– 14) mm long, lobes (2.2 –) 3.5 – 5.5 (– 6.5) mm long, palate raised with a central groove, pubescent along the groove. Stamens attached in distal half of corolla tube; filaments free for 3.5 – 4 mm, glabrous; anther thecae superposed and separated by 0.5 – 1 mm, somewhat oblique, each 0.95 – 1.4 mm long. Ovary glabrous or with minute glandular hairs; style 11 – 15 mm long, glabrous or with few hairs towards base; stigma capitate, 0.25 – 0.5 mm wide. Capsule 10 – 17.5 mm long, with sparse glandular hairs ± 0.5 mm long or glabrous. Seeds 2.4 – 2.8 × 1.8 – 2.4 mm, with numerous elongate, ± curved tubercles, longest towards the rim, with minute hair-like processes. Figs 1A, 2A & B, 3L – U & 4A. DISTRIBUTION. Endemic to the Cameroon Highlands, recorded in SE Nigeria, Bioko and W Cameroon. Map 1. SPECIMENS EXAMINED. NIGERIA. Ogoja Prov.: Cross River State, Obudu Cattle Ranch, fl. 30 Aug. 1955, Stone 78 (K!). EQUATORIAL GUINEA. Bioko: without precise locality, fl. Nov. 1860, Mann 579 (K!); San Carlos, Musola, fl. & fr. Oct. 1911, Mildbraed 6981 (B!, HBG!); Moka, fl. & fr. Nov. 1911, Mildbraed 7074 (HBG!); El Pico, fl. & fr. 10 Dec. 1951, Boughey 180 (K!); SW of Lago Biao, c. 5 miles, fl. 24 Sept. 1959, Melville 659 (BM!, K!); Cascadas Trail, fl. 11 March 2007, Luke et al. 11807 (EA, K!). CAMEROON. Southwest Prov.: Mt Cameroon, fl. & fr. Nov. 1862, Mann 1972 (K!); [Mt] Cameroon, upper slopes, fl. 1886, Johnston 62 (K!); near Mimbia, fl. 9 Oct. 1891, Preuss 1062 (lectotype K!); Mt Cameroon, Litoko, fl. & fr. 16 Dec. 1929, Maitland s.n. (K!); Mt Cameroon, Esele, fr. Feb. 1930, Maitland 1022 (K!); Manns-Quelle am Grossen Kamerunberg, fl. Nov. 1935, Zumpt s.n. (HBG!); Mt Cameroon, between Lyonga and Jongo, above Mimbia, fl. 24 March 1948, Brenan et al. 9366 (K!); Mt Cameroon, 1.5 miles NW of camp at Mann’s Spring, fl. 31 March 1948, Brenan & Jones 9555 (K!); Mt Cameroon, Mann’s Spring, fl. & fr. 28 Dec. 1958, Morton K839 (K!); Mt Cameroon, above Batoke, in bud 29 Dec. 1983, Thomas 2832 (MO, YA!); near Mbu-Bakundu village, fl. & fr. 12 Nov. 1986, Mambo & Thomas 235 (K!, MO); Buea, TB2 Bwassa, fl. 14 Sept. 1992, Tekwe 317 (K!, SCA, YA); Buea, path from TB1 to Mapanja, fl. 27 Sept. 1992, Tekwe 292 (K!, SCA, YA); Mt Cameroon, Mann’s Spring, fl. 10 Oct. 1992, Cheek 3684 (K!, SCA, YA); Mt © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 KEW BULLETIN VOL. 66(3) Cameroon, Bakingili – Nja Keta path, fl. 25 Oct. 1992, Thomas et al. 9170 (K!, SCA, YA!); Etinde, Mapanja – Batoke path, fl. 26 Oct. 1992, Mbatchou (Tchouto) 429 (K!, SCA, WAG, YA); Mt Kupe, Max’s Trail leading from Nyasoso to summit, fl. & fr. 22 Nov. 1994, Lane 238 (K!, SCA, YA); Etinde, above Likombe, path to summit, fl. 1 March 1995, Cable 1397 (K!, SCA); W of Kodmin up to 3 km along road to Loh Mt, fl. & fr. 12 Nov. 1998, Cheek 9582 (BR!, K!, KUPE, P, SCA, WAG, YA); Northwest Prov.: Bafut-Ngemba Forest Reserve, fl. & fr. 25 Feb. 1958, Hepper 2172 (K!); Kilum summit, fl. 11 April 1996, Cheek (photo. record); Bui Division, Elak, Transect KJ, fl. & fr. 28 Oct. 1996, Buzgo 621 (K!, WAG, YA). HABITAT. Recorded from mid-altitude to montane forest (500 – 3000 m alt.) including the understorey of undisturbed forest, amongst dense herbage in forest clearings and at the upper forest / grassland transition, and sometimes in disturbed forest and secondary scrub. It is usually terrestrial but rarely epiphytic on moist tree trunks. It is often recorded as locally common or dominant where found; for example M. Cheek (9582) recorded it as “extremely common in area of juju initiation for children” at Kodmin in the Bakossi Mts of Cameroon. This suggests that the species is gregarious, supporting the possibility that this species is plietesial (see introduction). Indeed, this species is most common on Mt Cameroon which supports a well-developed plietesial Acanthaceae community on its south side including Mimulopsis solmsii Schweinf., Brachystephanus giganteus Champl. (syn. Oreacanthus mannii C. B. Clarke) and Isoglossa spp. (Thomas 1996). Furthermore, this species has only been collected once on Mt Kupe, from Max’s Trail above Nyasoso in 1994 (Lane 238). This area was intensively surveyed in 1995 and 1996 and the lack of any further specimens of this species from Mt Kupe supports the postulated gap of several years between flowering. CONSERVATION STATUS. This species is widespread and locally common within the Cameroon Highlands, particularly on Mt Cameroon. Whilst high altitude sites such as the upper slopes of Mt Cameroon and Mt Oku are reasonably secure, lower altitude forest, particularly that under 1000 m alt., is threatened throughout its range. The assessment of Near Threatened (NT) given by Vollesen & Darbyshire (2004) is upheld. NOTES. Although flower and fruit size are rather variable in this species, the flower shape is constant and distinctive, as are the short, rather blunt calyx lobes, the inflorescence indumentum of conspicuous glandular hairs only, the rounded or cordate leaf base and the striking seed sculpturing (Fig. 2A & B). In addition, the pollen sculpturing differs somewhat from other Isoglossa species in the region, with the periporal zone more undulate (Fig. 1A). THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA 431 Fig. 4. A Isoglossa glandulifera, detail of flower, Cascadas Trail, Bioko, 11 March 2007 (photo. by W. R. Q. Luke). B I. dispersa, massflowering at Simandou, Guinée, Nov. 2010. C I. dispersa, mass-flowering at Mt Béro, Guinée, together with Brachystephanus oreacanthus (foreground), Jan. 2011. D I. dispersa, flowering spike, Simandou, Nov. 2010. PHOTOS BY P. K. HABA. Luke et al. 11807 from Bioko is unusual in having numerous fine hairs on the upper leaf surface in addition to the typical multicellular hairs. This specimen also has the most dense inflorescence indumentum. However, it is otherwise a good match for I. glandulifera (see Fig. 4A). 2. Isoglossa nervosa C. B. Clarke (1900: 229); Heine (1963: 424); Lebrun & Stork (1997: 484); Cable & Cheek (1998: xxxviii); Vollesen (1998: 3). Type: Cameroon, Mt Cameroon, Mann 2009 (lectotype K sheet 1!, selected here; isolectotypes K sheets 2 – 4!). Isoglossa sp. B sensu Heine (1963: 424), quoad Guinea 2953 ex [Fernando Po] Bioko; Lebrun & Stork (1997: 484). Isoglossa sp. aff. glandulifera sensu (Vollesen & Ghogue 2000: 112), non Lindau. Perennial herb, erect or ascending to weakly so, 30 – 150 cm tall, lowermost stems often trailing and rooting at the nodes. Stems quadrangular when young, sulcate between the angles, with two opposite lines of pilose or antrorse-pubescent hairs, sometimes restricted to immediately below the nodes, later (rarely early) glabrescent. Leaves (excluding uppermost pairs) ovate or elliptic, 4.5 – 12 × 2.3 – 6.5 cm, base attenuate or with a narrowly cuneate wing-like extension, apex acuminate or attenuate, midrib above, margin and veins beneath usually pubescent, often with scattered short hairs between the veins above, these appearing © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 432 KEW BULLETIN VOL. 66(3) Map 1. Distribution of Isoglossa glandulifera. deflated in dried material, sometimes with few short glandular hairs beneath, rarely largely glabrous; lateral veins (5 –) 6 – 9 pairs; petiole 1 – 6 cm long, usually conspicuously pilose above, rarely glabrous; upper© The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 most pairs of leaves broadly ovate with a cordate base, often sessile and ± reduced. Inflorescence terminal (often also with reduced lateral inflorescences), a lax panicle, pyramidal to narrowly so in outline, 9 – 40 × THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA 2.5 – 20 cm, many-branched at maturity, branching along main axis usually opposite, cymules sometimes partially secund; axes puberulous and glandular, at first the glands sparse and short-stalked, becoming ± densely glandular-pilose or -pubescent at maturity, hairs then 0.5 – 1 mm long, gland tips capitate, axes often also with scattered or numerous long wispy eglandular hairs to 2.5 mm long; main axis bracts foliaceous in the lower portion or at the lowermost node only, ovate to lanceolate, 7 – 32 × 3 – 16 mm, then ± gradually (rarely rapidly) reducing in size upwards, those at the midpoint of the axis lanceolate, subulate or narrowly elliptic, (1.5 –) 2.5 – 20 × 0.5 – 4.5 (– 8) mm, apex acute; bracteoles linear-lanceolate, 1 – 3 mm long; pedicels 0.5 – 1.5 mm long. Calyx lobes linear-lanceolate, 2 – 6 mm long in flower, extending to 3.5 – 6.5 mm in fruit, indumentum as axes. Corolla 11.5 – 19 mm long, white or pink, with red or pink markings on palate of lower lip; shortly pubescent externally at least on the dorsal side, glabrous internally; tube campanulate or narrowly so, 5 – 8.5 mm long, 1 – 2 mm wide at base, ventral side declinate, sometimes slightly ventricose beyond attachment point of stamens, (2.3 –) 3 – 5 mm wide at mouth; upper lip triangular, 4 – 6.5 mm long, lobes reflexed, 1 – 2 mm long; lower lip somewhat protruding, (5 –) 6.5 – 11 mm long, lobes 2 – 5 mm long, palate raised with a central groove, glabrous. Stamens attached in distal half of or midway along the corolla tube; filaments free for 3 – 4.5 mm, glabrous; anther thecae superposed, slightly overlapping or separated by up to 0.6 mm, subparallel, each 0.9 – 1.4 mm long. Ovary glabrous or with few minute hairs; style (4.5 –) 5.5 – 7.5 mm long, glabrous or pubescent in lower half; stigma ellipsoid, 0.15 – 0.25 mm wide. Capsule 9 – 11 mm long, puberulous and often with scattered short-stalked glands and/or long eglandular hairs. Seeds 1.7 – 2.4 × 1.2 – 1.6 mm, with elongate glochidiate tubercles most dense towards the rim. Figs 1B, 2C & D & 3A – K. DISTRIBUTION. Endemic to the Cameroon Highlands, recorded in SE Nigeria, Bioko and W Cameroon. Map 2. SPECIMENS EXAMINED. NIGERIA. Taraba State: Mambilla, Ngeliyaki, fl. 26 Nov. 1975, Ekwuno 297 (K!, FHI!). EQUATORIAL GUINEA. Bioko: Pico de Sta. Isabel, fl. & fr. 2 March 1947, Guinea 2953 (K!); carretera del pico Basilé, km 18, fl. 11 Nov. 1986, Carvalho 2682 (B!, BR!, K!). CAMEROON. Southwest Prov.: Mt Cameroon, fl. Dec. 1862, Mann 2009 (lectotype K!; isolectotype K!); Mt Cameroon, upper slopes, fl. 1886, Johnston 63 (original syntype K!); Mt Cameroon, to N of path from Hut 1 to Hut 2, fl. & fr., without date, Morton K801 (K!); Mt Cameroon, c. 3 miles W of Mann’s Spring, fl. 28 Dec. 1958, Morton K860 (K!); Mt Cameroon, fr. 1 Oct. 1983, Thomas 2626 (K!, MO, P!, YA!); Mt Cameroon, upper southern slopes, fl. 5 Oct. 1992, Thomas 9333 (K!, SCA, YA!); Mt Cameroon, 433 hunters’ path going W of Mann’s Spring, over 1983 lava flow, through Wikile, fl. 4 Nov. 1993, Cheek 5355 (BR!, K!, MO, SCA, WAG, YA); Northwest Prov.: piste du village d’Okou au Mt Oku [Okou], fl. 14 July 1967, Letouzey 8936 (BR!, K!, P!, YA!); Mt Oku, fl. 29 Oct. 1996, Munyenyembe 794 (BR!, K!, SCA!, WAG!, YA!); West Prov.: [Bambuto] Bamboutos Mts, fl. & fr. Dec. 1938, Jacques-Félix 2849 (P!); Bamboutos Mts, c. 20 km N of Dschang, fl. & fr. 27 Nov. 1974, Letouzey 13371 (YA!). Adamoua Prov.: Mt Daland, ouest Sambolabo, fl. 6 Nov. 1967, Jacques-Félix 9092 (K!, P!). HABITAT. Recorded from montane forest of Podocarpus, Prunus, Myrsine, Nuxia and Syzygium, bamboo thicket, upper forest-grassland transition thickets and in adjacent montane grassland; alt 2000 – 3000 m. It almost certainly has a plietesial ecology (see Introduction). CONSERVATION STATUS. This species is listed by IUCN (2009) as Vulnerable (VU D2) based upon the assessment in Cable & Cheek (1998). At that time, it was considered to be endemic to Mt Cameroon. It is now known to be more widespread in the Cameroon Highlands, being present on most of the high peaks, with eight localities known and an AOO estimated at 32 km2. However, whilst the Mt Cameroon and Mt Oku sites appear to be secure from disturbance, those on the Bamboutos Mts and the Mambilla Plateau are under great threat of clearance from agriculture, if not already lost. A further potential threat to whole populations is through stochastic events during the long maturity cycle of this plietesial taxon, for example fire-damage at the seedling stage. It is therefore reassessed here as Vulnerable (VU B2ab(iii, iv) + c(iv)). NOTES. This species is closely allied to Isoglossa membranacea C. B. Clarke, described from Malawi. Clarke (1900) in fact described both species in the same publication but had seen only flowering material of each and he did not remark upon their similarity. In fact, he rather unhelpfully keyed out the west African species purely on geography with no supporting characters. With fruiting material now available, the affinity is clear. They share hairy capsules, seeds with elongate-glochidiate tubercles (Fig. 2C & D), similar inflorescence indumentum and corolla shape, and leaves with a cuneate-attenuate base which can form a wing along the upper petiole (although often less pronounced in I. nervosa). Two subspecies are currently recognised in I. membranacea: subsp. membranacea from the Misuku Hills of N Malawi and subsp. septentrionalis I. Darbysh. from S Sudan and NE Congo-Kinshasa through Uganda to W Kenya (Darbyshire 2009). Rather surprisingly, I. nervosa appears closest to the former. Well-developed specimens of I. nervosa are readily separable from those of I. membranacea by having one or more of the following characters: larger corollas, larger and leafy main axis bracts in the lower portion of the inflorescence and/or the stems being hairy when young (see key © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 434 KEW BULLETIN VOL. 66(3) Map 2. Distribution of Isoglossa nervosa (●) and I. sp. A (★). below). In addition, the leaf veins are typically more prominent beneath in I. nervosa. However, all these characters are rather variable and no single one of them is wholly diagnostic in isolation. Small (perhaps immature?) plants of I. nervosa can appear very close to I. membranacea sensu stricto and JacquesFelix 9092 from Adamoua, Cameroon is largely inseparable. Isoglossa nervosa could therefore be considered a further subspecies of I. membranacea but we keep them separate here based on the notable differences in the majority of the material. Whilst the disjunction is great, I. nervosa occupies largely the same habitat as I. membranacea, that of very wet Afromontane forest. Key to Isoglossa nervosa and I. membranacea Corolla to 19 mm long, often over 13 mm (min. 11.5 mm); main axis bracts usually foliaceous in the lower portion of the inflorescence where typically ovate to lanceolate, 7 – 32 mm long; young stems usually hairy in two lines at least immediately below the nodes; Cameroon Highlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. nervosa Corolla 7.5 – 13 mm long; main axis bracts minute throughout the inflorescence, (triangular-) lanceolate, to 2.5 mm long; stems essentially glabrous; S Sudan and NE Congo to N Malawi . . . . . . . . . . . . . I. membranacea © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA 3. Isoglossa dispersa I. Darbysh. & L. J. Pearce sp. nov. I. nervosae similis sed foliis majoribus 15.5 – 25.5 cm (non 4.5 – 12 cm) longis, pilis glandulosis inflorescentiae subsessilibus (non manifeste stipitatis) ad maturitatem glande ad apicem ellipsoidea (non capitata) instructis, corolla extus glabra (non dorsaliter ut minimum pubescenti), capsula glabra (non puberula glandibus breviter stipitatis neque pilis longis eglandulosis instructa) et tuberculis seminum brevibus (non elongato-glochidiatis) processus minutos curvatos ferentibus differt. Typus: Cameroon, rive droite de la Metchum [R.] près Obang, 18 km S Wum, Letouzey 13424 (holotypus YA sheet 1!; isotypi K!, YA sheet 2!). http://www.ipni.org/urn:lsid:ipni.org:names:77114304-1 Isoglossa sp. A sensu Heine (1963: 424), quoad Lightbody in FHI 26290 ex Cameroon; Lebrun & Stork (1997: 484). Isoglossa sp. C sensu Heine (1963: 424), quoad T. S. Jones 117 ex Sierra Leone; Lebrun & Stork (1997: 484). Perennial herb or subshrub, erect or ascending, 40 – 250 cm tall, lowermost stems sometimes trailing and rooting at the nodes. Stems quadrangular when young, sulcate between the angles, subterete with age, glabrous. Leaves (excluding uppermost pairs) elliptic or oblong-elliptic, 15.5 – 26 × 6 – 14 cm, base ± oblique, cuneate or attenuate, apex acuminate, glabrous except for inconspicuous short antrorse hairs along margin and sometimes main veins beneath; lateral veins 8 – 10 pairs; petiole 2 – 11.5 cm long, glabrous; uppermost pair(s) of leaves ovate, sessile and with a cordate base, ± reduced. Inflorescence terminal, a lax panicle, pyramidal to narrowly so in outline, 16 – 35 × 3 – 20 cm, many-branched at maturity, branching along main axis usually opposite, that on the lateral branches opposite to partially 1-sided, cymules sometimes partially secund; axes with numerous (sub) sessile ellipsoid glands, and minutely eglandularpuberulous (glands can be absent in immature inflorescences), with or without scattered long patent eglandular hairs to 2 mm, main axis often largely glabrous in lower portion; main axis bracts subulate or slightly oblanceolate, 2.5 – 8.5 × 0.5 – 1.3 mm, apex acute; bracteoles as bracts but 1.5 – 4 mm long; pedicels 0.5 – 1.5 mm long in flower, to 2.5 mm in fruit. Calyx lobes linear-lanceolate, 1.7 – 4 mm long in flower, extending to 3 – 6.5 mm in fruit, indumentum as axes, short eglandular hairs restricted to lobe margins. Corolla (9.5 –) 12 – 16 mm long, white or tinged pink to purple outside, with violet or ?yellow markings on palate of lower lip and/or throat; glabrous externally except for few cilia at apex of lower lip, tube pubescent internally below attachment point of stamens; tube subcampanulate, (4 –) 6 – 7.5 mm long, 1 – 1.8 mm wide at base, ventral portion 435 somewhat ventricose above attachment point of stamens, (3 –) 4 – 5 mm wide at mouth; upper lip triangular, (4 –) 4.5 – 6.5 mm long, lobes somewhat reflexed, (0.8 –) 1.8 – 2.5 mm long; lower lip protruding, (5 –) 6 – 8.5 mm long, lobes (1.5 –) 3 – 3.5 mm long, palate raised and with a central groove, glabrous or sparsely pubescent. Stamens attached in upper half of corolla tube; filaments free for (2 –) 2.5 – 3.2 mm, glabrous; anther thecae superposed and separated by 0.3 – 0.5 mm, parallel or somewhat oblique, upper theca 0.7 – 1.1 mm long, lower theca 0.65 – 0.95 mm long. Pistil glabrous; style 4 – 5 mm long; stigma globose in outline, 0.15 – 0.25 mm wide. Capsule 11 – 16 mm long, glabrous. Seeds 2 – 3 × 1.8 – 2.6 mm, with numerous somewhat elongate tubercles, these with minute curled processes, most conspicuous when immature. Figs 1C, 2E & F, 4B – D & 5. DISTRIBUTION. Recorded from the lower slopes of the Guinea (Loma-Man) Highlands in Guinée and Sierra Leone, and the Cameroon Highlands. Map 3. SPECIMENS EXAMINED. GUINÉE. Simandou Range, NW du pic de Dabatini, sud du village Lamadou, fl., fr., Jan. 2010, P. K. Haba 647 (K!, NHGC! WAG!); Simandou, western spur, fl. Nov. 2010, P. K. Haba (photos.); Mt Béro, Foodjou village, fl. & fr. Jan. 2011, P. K. Haba et al. (photos.). SIERRA LEONE. Northern Prov.: Bintumane Peak, fl. bud & fr. 10 Jan. 1951, T. S. Jones 117 (K!). CAMEROON. Northwest Prov.: NkonWum Reserve, woodland along R. Mete, fl. & fr. 23 Jan. 1951, Lightbody in FHI 26290 (B!, K!); vallon forestier au sud de Berabe, 10 km NNE Nkambe, fl. 12 Nov. 1974, Letouzey 13201 (BR!, K!, P, YA!); rive droite de la Metchum [R.] près Obang, 18 km S Wum, fl. & fr. 3 Dec. 1974, Letouzey 13424 (holotype & isotype YA!, isotype K!). West Prov.: Plaine des Mbos Plain à 14 km au sud de Dschang, fl. & fr. 17 Dec. 1981, Nkongmeneck 194 (P!, YA). HABITAT. Recorded from forest understorey, including along path margins and in secondary forest, and along streams and rivers in shade; alt. 550 – 1150 m. In Guinée it forms large colonies, running to millions of individuals within a population (see Introduction). CONSERVATION STATUS. Known from only seven sites historically, with an estimated AOO of 30 km². Human population pressure is high within its range in Cameroon and much of the forest has already been lost there. Only the Sierra Leone site is currently protected, falling within the Loma Mts National Park. This species is therefore considered Vulnerable (VU B2ab(iii)), but this assessment would need upgrading to Endangered if it proves to have been lost from some of its historical sites. The sites at Lamadou and Mt Béro in Guinée and Metchum in Cameroon are strong contenders for formal conservation protection in view of the presence of both this species and the extremely © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 436 KEW BULLETIN VOL. 66(3) Fig. 5. Isoglossa dispersa. A habit, inflorescence and mature leaves; B indumentum of upper portion of inflorescence axis; C detail of inflorescence glands; D flower in situ; E dissected corolla with stamens; F detail of anthers, rear and front views; G dehiscing fruit with immature seeds; H immature seed; J detail of seed tubercles; K mature seed with worn tubercles. A – F from Letouzey 13424, G – K from Jones 117. DRAWN BY ANDREW BROWN. © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 437 THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA Map 3. Distribution of Isoglossa dispersa. rare Brachystephanus oreacanthus Champl. (see note below), although the Cameroon site may already have been lost. ETYMOLOGY. The species epithet “dispersa” (dispersed or scattered) refers to the apparent disjunction in distribution of over 2000 km between the two population centres of this species. NOTES. This species is easily separated from all others in the Isoglossa dichotoma complex by the combination of very large leaves, glabrous corollas and capsules, and the unusual indumentum on the mature inflorescences in which the glandular hairs are subsessile and with an ellipsoid gland-tip, giving the inflorescence axes a papillose appearance (Fig. 5B & C) and rendering the whole inflorescence white in living material (Fig. 4B – D). Mature fruiting specimens of this species usually have a few corollas which are noticeably smaller than in flowering material. This is most striking in Lightbody in FHI 26290 in which the flowers are represented by the bracketed lower measurements in the description. In this specimen the corollas do not appear to fully open and, on sampling the anthers for pollen content, were found to contain rather few intact grains, although this may be due in part to the fact that this specimen has been infected by mould. It is possible that this species produces cleistogamous flowers at the fruiting stage, an occurrence not uncommon in the Acanthaceae. Whilst the disjunction in the distribution of this species is unusual, it is not unique. In fact, a remarkably similar disjunction has been recorded in Brachystephanus Nees, the sister genus to Isoglossa. B. oreacanthus Champl. was until recently known from only two collections, one in W Cameroon and a second in SE Guinée, on both occasions in the same locality (or very nearby) as I. dispersa (Champluvier & Darbyshire 2009). B. oreacanthus has since been recorded growing in mass-flowering populations together with I. dispersa at both Simandou and Mt Béro in Guinée (P. K. Haba, pers. comm.; Fig. 4C). 4. Isoglossa sp. A (= Letouzey 13152) Slender perennial herb, 15 – 150 cm tall, decumbent, lower portion of stems trailing and rooting at the nodes. Stems with 4 shallow ridges in 2 opposite pairs, shortly antrorse and/or retrorse-puberulous mainly along the ridges. Leaves somewhat anisophyllous; blade (excluding uppermost pairs) elliptic or ovate-elliptic, 6.8 – 9 × 2.7 – 4.6 cm, base (cuneate-) attenuate, apex acuminate, glabrous except for inconspicuous short antrorse hairs along the midrib beneath and on the margin towards the base; lateral veins 5 – 7 pairs; petiole 1 – 2 cm long, antrorse-puberulous on the ridges above; uppermost pair(s) of leaves broadly ovate and often sessile with a cordate or rounded © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 438 base. Inflorescence terminal, a lax slender panicle, pyramidal to oblong in outline, (3.5 –) 9 – 19 × (1 –) 2.5 – 9 cm, branching along main axis opposite or partially 1-sided, cymules sometimes partially secund; axes eglandular-puberulous and with interspersed minute glandular hairs 0.1 – 0.2 mm long, the gland tip capitate; main axis bracts linear-lanceolate, 1 – 2 × 0.3 – 0.5 mm, apex acute; bracteoles as bracts but to 1 mm long; flowers and fruits subsessile. Calyx lobes linear-lanceolate, 1.4 – 2 mm long in flower, extending to 2.8 – 4.5 mm in fruit, indumentum as axes. Corolla 5.5 – 8 mm long, white or cream, with violet markings on palate of lower lip; glabrous externally; tube subcylindrical, 3 – 3.3 × 1.7 mm; upper lip triangular, 1.5 – 2.7 mm long, reflexed distally, lobes ± 0.7 mm long; lower lip protruding, 2.5 – 4.5 mm long, lobes 1 – 2.5 mm long, palate raised with a central groove and with prominent “herring-bone” patterning, glabrous. Stamens attached ± midway along the tube; filaments free for 1 – 1.25 mm, glabrous; anther thecae strongly offset but slightly overlapping, each 0.7 – 0.8 mm long. Pistil glabrous; style 1 – 1.3 mm long; stigma ellipsoid in outline, 0.15 – 0.2 mm wide. Capsule 9 – 13 mm long, glabrous. Seeds ± 2.5 × 2 mm, rugosetuberculate. Figs 1D & 2G & H. DISTRIBUTION. A species of the Guineo-Congolian regional centre of endemism, known only from Cameroon and the Central African Republic. Map 2 (stars). SPECIMENS EXAMINED. CAMEROON. Northwest Prov.: entre Berobi et Adu, 18 km NNE Nkambe, fl. & fr. 6 Nov. 1974, Letouzey 13152 (BR!, K!, YA!). Central Prov.: [Jaunde] Yaoundé, fl. Jan. 1914, Mildbraed 7845 (B†, K!). CENTRAL AFRICAN REPUBLIC. Bimbo Forest, 35 km SW of Bangui, fl. & fr. 8 Dec. 1969, Hepper 4110 (K!). HABITAT. Recorded from lowland rainforest and gallery forest; the Letouzey collection was made at 300 m alt. CONSERVATION STATUS. Known only from the three specimens cited, with the historic Yaoundé site likely to have been lost through extensive deforestation in the vicinity of this city. It was not recorded during recent intensive botanical survey of Mefou Proposed National Park, one of the largest remnant forest patches in the Yaoundé area (M. Cheek, pers. comm.). It is therefore likely to be threatened but is currently considered Data Deficient (DD) pending a complete understanding of its taxonomic status. NOTES. The three specimens cited are separated from the other west African species by the combination of the rugose-tuberculate seeds (the tubercles not elongate as in the other species — Fig. 2), the very short bracts and the differing stem indumentum. It appears superficially close to Isoglossa lactea Lindau from the east African mountains but that species differs in the stem hairs (if present) being restricted to two opposite furrows (see Darbyshire 2009: Fig. 3L), the leaves © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011 KEW BULLETIN VOL. 66(3) usually having more lateral nerves (up to 12 pairs) and the fruits usually being larger (to 18.5 (– 20) mm long) with a more acuminate apex and drying a rich chestnut brown, not pale greenish-brown as in I. sp. A. An additional difference to other west African species is the very small corollas. However, the two good specimens seen to date (Hepper 4110 & Letouzey 13152; the Mildbraed collection is depauperate) are at the fruiting stage with only a few corollas remaining. It is quite possible that these flowers are abnormally small, as in the fruiting specimens of Isoglossa dispersa (see note to that species), and we may well not have seen fully developed corollas. It is for this reason that we are hesitant to describe this species based on the material currently available. Acknowledgements We would like to thank Martin Cheek and two anonymous reviewers for comments on a draft of this manuscript, Katherine Challis for providing the Latin diagnosis for Isoglossa dispersa, Andrew Brown for the excellent illustrations and Quentin Luke and Pierre Haba for allowing us to use the photographs reproduced here. Pierre Haba, Pepe Haba, Alphonse Goman, Cece Jérôme and colleagues in the Environment team at Rio Tinto Guinea (SIMFER) are also thanked for providing excellent information on the populations of Isoglossa dispersa and Brachystephanus oreacanthus at Simandou and Mt Béro; it is hoped that with Rio Tinto’s assistance these populations and the important forest ecosystems within which they are found can be safeguarded for the future. The following are thanked for providing a loan of/access to the Isoglossa collections at their respective institutions: Robert Vogt (B), Jonathan Gregson (BM), Elmar Robbrecht (BR), Geoffrey Mwachala (EA), HansHelmut Poppendieck (HBG), Marc Pignal (P) and Jean-Michel Onana (YA). References Cable, S. & Cheek, M. (1998). The Plants of Mt Cameroon. A Conservation Checklist. Royal Botanic Gardens, Kew. Champluvier, D. & Darbyshire, I. (2009). A revision of the genera Brachystephanus and Oreacanthus (Acanthaceae) in tropical Africa. Syst. Geogr. Pl. 79: 115 – 192. Cheek, M. (2004). Foreword. In: M. Cheek, B. J. Pollard, I. Darbyshire, J.-M. Onana, & C. Wild (eds), The Plants of Kupe, Mwanenguba and the Bakossi Mountains, Cameroon. A Conservation Checklist. Royal Botanic Gardens, Kew. Clarke, C. B. (1900). Acanthaceae. In: W. Thiselton-Dyer (ed.), Flora of Tropical Africa 5 (2): 227 – 234. L. Reeve & Co., London. THE GENUS ISOGLOSSA (ACANTHACEAE) IN WEST AFRICA Darbyshire, I. (2009). Taxonomic notes and novelties in the genus Isoglossa (Acanthaceae) from east Africa. Kew Bull. 64: 401 – 427. Hansen, B. (1985). Taxonomic revision of the S. E. Asian species of Isoglossa (Acanthaceae). Nordic J. Bot. 5: 1 – 13. Heine, H. (1963). Acanthaceae. In: F. N. Hepper (ed.), Flora of West Tropical Africa 2nd ed. 2: 391 – 432. Royal Botanic Gardens, Kew. IUCN (2001). IUCN Red List Categories and Criteria. Version 3.1. IUCN Species Survival Commission, IUCN, Gland, Switzerland and Cambridge, U.K. ____ (2009). IUCN Red List of Threatened Species. Version 2009.2. http://www.iucnredlist.org/. Accessed 18 Nov. 2009. ____ Standards and Petitions Working Group (2008). Guidelines for Using the IUCN Red List Categories and Criteria. Version 7.0. Prepared by the Standards and Petitions Working Group of the IUCN SSC Biodiversity Assessments Sub-Committee in August 2008. Downloadable from http://intranet.iucn.org/ webfiles/doc/SSC/RedList/RedListGuidelines.pdf. Accessed 22 March 2010. Kiel, C. A., McDade, L. A., Daneil, T. F. & Champluvier, D. (2006). Phylogenetic delimitation of Isoglossinae (Acanthaceae: Justicieae) and relationships among constituent genera. Taxon 55: 683 – 694. 439 Lebrun, J.-P. & Stork, A. L. (1997). Énumération des plantes à fleurs d’Afrique Tropicale. Vol. IV — Gamopetales: Clethraceae à Lamiaceae. Conservatoire et Jardin botaniques de la ville de Genève. Lindau, G. (1894). Acanthaceae Africanae 2. Bot. Jahrb. Syst. 20: 1 – 76. ____ (1895). Acanthaceae. In: A. Engler & K. Prantl (eds), Die Natürlichen Pflanzenfamilien 4(3b): 274 – 354. Engelmann, Leipzig. Poriazis, D. L. & Balkwill, K. (2008). Developmental variation in a species of Isoglossa (Acanthaceae: Ruelliodeae) over a season. Bothalia 38: 131 – 140. Thomas, D. (1996). Synchronously flowering monocarpic Acanthaceae in the montane forests of Cameroon. Acanthus 6: 2. Vollesen, K. (1998). Acanthaceae. In: S. Cable & M. Cheek (eds), The Plants of Mt Cameroon. A Conservation Checklist, pp. 1 – 6. Royal Botanic Gardens, Kew. ____ & Darbyshire, I. (2004). Acanthaceae. In: M. Cheek, B. J. Pollard, I. Darbyshire, J.-M. Onana, & C. Wild (eds), The Plants of Kupe, Mwanenguba and the Bakossi Mountains, Cameroon. A Conservation Checklist. Royal Botanic Gardens, Kew. ____ & Ghogue, J-P. (2000). Acanthaceae. In: M. Cheek, J.-M. Onana & B. J. Pollard (eds), The Plants of Mount Oku and the Ijim Ridge, Cameroon. A Conservation Checklist, pp. 111 – 113. Royal Botanic Gardens, Kew. © The Board of Trustees of the Royal Botanic Gardens, Kew, 2011