One of the authors (AH) discovered a new species of Rhipidoglossum (Epidendroideae subtribe Angraecinae) in montane forest in the botanically poorly collected Pare mountains of north-eastern Tanzania. It belongs to a small group of species previously assigned to the genus Margelliantha P.J.Cribb (1979) and is distinguished by its dwarf habit, short stem and short inflorescence of few campanulate flowers with a concave lip that is broader than long and a clavate to globose spur. The East African species of Margelliantha have recently been subsumed in a broadly defined Rhipidoglossum by Farminhão et al. (2018) based upon extensive DNA analysis.

The new species described here is similar to Rhipidoglossum leedalii (P.J.Cribb) Farminhão & Stévart which occurs in the Nguru, Uluguru and Udzungwa mountains of Tanzania but differs in several features listed below. Rhipidoglossum clavatum (P.J.Cribb) Farminhão & Stévart is endemic to the Usambara Mountains, to the east of the Pare mountains, while R. globularis (P.J.Cribb) Farminhão & Stévart occurs in the Uluguru mountains.

Rhipidoglossum pareense P.J.Cribb & Hemp sp. nov. Type: Tanzania, Pare Mountains, Mwala, 1760 m, 14 March 2019, A. Hemp 7304 (holotype K, isotypes B, MO, NHT, UBT).

http://www.ipni.org/urn:lsid:ipni.org:names:77297411-1

A dwarf epiphytic herb; roots slender, clustered at base of stem, 1 mm diam. Stem short, up to 2.5 cm long, covered by imbricate leaf bases. Leaves narrowly oblanceolate, obliquely acute at tip, 8 – 11 cm × 9 – 11 mm, sheathing at the base, dull green but paler beneath. Inflorescences 1 – several, shorter than the leaves, 3.3 – 5.5 cm long, subdensely usually 8- to 12-flowered; peduncle slender, wiry 12 – 25 mm long, bearing 1 or more amplexicaul sterile bracts along length; rachis slender, 1.5 – 4.5 cm long; bracts amplexicaul at base, ovate, acute, 1 – 1.5 mm long. Flowers glistening white with a greenish ovary and dark green anther cap; pedicel and ovary 5 – 6.8 mm long. Dorsal sepal cucullate, elliptic, rounded, 2 – 2.8 × 1.2 – 1.5 mm; lateral sepals very obliquely ovate, acute, 3 – 3.5 × 2 mm. Petals subcircular-broadly ovate, rounded at tip, 3.2 × 2.5 mm. Lip slightly concave, broadly obovate-circular, obtuse or very slightly emarginate, 3.5 – 4.4 × 4.5 – 6 mm, lacking a callus, margins erose; spur incurved clavate, 3.15 – 4 mm long. Column 1 – 1.5 mm long, with a column-foot; rostellum 3-lobed, the mid-lobe oblong, obtuse, the side lobes shorter than the mid-lobe, triangular; pollinia 2, each attached to a viscidium by a slender, linear stipe, the two viscidia confluent along their inner margins until maturity.

recognition. The allied species of Rhipidoglossum (formerly in Margelliantha) are closely related and distinguished by small but consistent differences. Rhipidoglossum pareense is most closely allied to R. leedalii (P.J.Cribb) Farminhão & Stévart which occurs in the Uluguru mountains and Southern Highlands of Tanzania but differs in having an inflorescence with up to 12 flowers (vs 4 – 8 flowers in R. leedalii), smaller flowers with a 2 – 2.8 mm long dorsal sepal (vs 3.5 – 4.5 mm), 3.5 mm long lateral sepals (vs 4 – 5 mm long), 3 – 3.2 × 2.5 – 3 mm petals (vs 4 × 3 – 3.5 mm), a broadly obovate-circular 3.5 – 5 × 4.5 mm lip (vs 5 – 5.5 × 6 – 8 mm) with a markedly erose front margin, 3.15 – 4.5 mm long spur (vs 5 – 7 mm) and shorter 5.2 – 6.8 mm long pedicel and ovary (vs 10 – 11 mm long). Figs 1 & 2.

Fig. 1
figure 1

Rhipidoglossum pareense. A habit; B inflorescence; C flower; D dorsal sepal; E lateral sepal; F petal; G lip; H column & lip, side view; J column & anther cap, front view; K column & anther cap, side view; L column, anther cap and pollinia removed; M anther cap, side view; N anther cap, ventral view; P pollinium. All from Hemp 7304 (type collection). drawn by judi stone.

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Fig. 2
figure 2

Rhipidoglossum pareense. A habit; B, C inflorescences. photos: a. hemp.

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distribution. Endemic to the South Pare and West Usambara mountains of north-eastern Tanzania. In montane, mossy mist forest: 1760 – 1950 m.

specimens examined. tanzania. T3, West Usambara mountains, Baga II Forest reserve, on main ridge of Kwagoroto, leading from the summit, 1950 m, 24 Feb. 1984, Borhidi, Demissew, Hedrén, Iversen, Mziray & Pócs 84121 (K, UPS). A collection (Archer 548. EAH) from Kasigau Hill in Teita district of Kenya needs reassessment and may belong to R. pareense rather than to R. leedalii.

habitat. This orchid occurs in the Pare mountains as an epiphyte in a montane, low-stature cloud forest at 1760 m (Fig. 3). Dominant associated trees and shrubs in the only 10 m high canopy include Syzygium micklethwaitii Verdc. subsp. subcordatum Verdc., Xymalos monospora (Harv.) Baill. ex Warb., Aphloia theiformis (Vahl) Benn., Agarista salcifolia (Lam.) G.Don, Psychotria goetzei (K.Schum.) Petit and Myrsine melanophloeos (L.) R.Br. A collection (Borhidi et al. 84121 (K, UPS)) from the West Usambara mountains, lying to the immediate East of the Pare Mountains, can also be attributed to Rhipidoglossum pareense. It was collected at 1950 m a.s.l. from montane, mossy forest dominated by trees of Syzygium, Ocotea usambarensis and Agauria.

Fig. 3
figure 3

Mossy, montane, low-stature cloud forest at Mwala (1760 m), the type locality in the Pare mountains of North-eastern Tanzania. photo: a. hemp.

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The climate of the type locality in the Pare mountains is humid and foggy (all following information unpub. data of A. Hemp). Mean annual rainfall is only about 1000 mm, however fog water interception provides more than twice of this amount in addition (data of 2 years). Consequently, mean annual relative humidity is 94%. Mean annual temperature is 15.7°C with a minimum temperature of 8.7°C and a maximum temperature of 29.0°C. Because of this high humidity, tree trunks and branches are densely covered by mosses (60% coverage) and vascular epiphytes (10% coverage). Rhipidoglossum pareense grows together with over 30 other epiphytic vascular plants, including the orchids Polystachya transvaalensis Schltr., P. caespitifica subsp. latilabris (Summerh.) P.J.Cribb & Podz., P. cultriformis (Thou.) Spreng., P. lindblomii Schltr., Sphyrarhynchus schliebenii Mansf. and many ferns and lycopods, e.g. Elaphoglossum tanganjicense Krajina ex Pic.Serm., E. acrostichoides (Hook. & Grev.) Schelpe, E. angulatum (Blume) Moore, Stenogrammitis strangeana (Pic.Serm.) Labiak, Huperzia dacrydioides subsp. dura (Pic.Serm.) Verdc., H. holstii (Hieron.) Pic.Serm., Hymenophyllum kuhnii C.Chr., Asplenium theciferum (Kunth) Mett., A. mannii Hook. and A. sandersonii Hook.

conservation status. VU. Rhipidoglossum pareense is known from one locality in the South Pare mountains and a second in the West Usambara mountains. In two research plots in the former (following the method of Braun-Blanquet 1964) of 0.1 ha each, 20 individuals were found. Based on this we estimate that the type locality hosts perhaps 600 mature individuals, since the very special habitat requirements of this epiphytic species are only realised on the very top of Mwala with about 6 hectares. With one locality, the Area of Occupancy is 4 km2 under the Red List Guidelines, which require the use of grid cells of 2 × 2 km to calculate AOO (IUCN Standards and Petitions Subcommittee 2022). The area where the species occurs is protected as Forest Reserve, and during our visit no illegal logging activities or other threats were observed. Even in the absence of threats, based on criterion D (IUCN 2012) Rhipidoglossum pareense must be regarded as Vulnerable (VU D1). No information exists on the population in the West Usambaras but, on the basis of the forest extent and destruction there, we suspect that its conservation status will not change once more information from there is available.

notes. Rhipidoglossum clavatum (P.J.Cribb) Farminhão & Stévart, found in the West Usambara mountains, to the east of the Pares, has greenish-yellow flowers, its petals are narrower than long and its lip is transversely elliptic and noticeably broader than long when flattened, with a small tooth in the mouth of the slender clavate spur much longer than the lip. Rhipidoglossum globulare (P.J.Cribb) Farminhão & Stévart from the northern Uluguru mountains is known only from the type collection. It has noticeably falcate leaves, larger 3 mm long bracts and creamy yellow flowers with a 5 × 6 mm flabellate lip with a 4 mm long spur with a globose tip. A key to distinguish R. pareense from close allies is provided below.

Key to East African species of the Rhipidoglossum leedalii complex

  • 1. Flowers creamy yellow; spur almost globose, 2.5 – 4 mm diam.; bracts somewhat inflated, 3.5 mm long, 3 mm wide...R. globularis

  • Flowers white with a green anther-cap or pale yellowish-green; spur clavate, more than 4 mm long, less than 2 mm diam.; bracts inconspicuous, less than 2.5 mm long and wide...2

  • 2. Flowers pale greenish-yellow; spur straight, less than 1.2 mm diam.; lateral sepals not markedly falcate...R. clavatum

  • Flowers glistening white with a green anther-cap; spur incurved, 2 mm diam. at apex...3

  • 3. Inflorescences 4 – 8-flowered; pedicel and ovary 10 – 11 mm long; sepals more than 4.5 mm long; lip more than 5 – 6 × 6 – 8 mm wide; spur 6 – 7 mm long...R. leedalii

  • Inflorescences usually 9 – 12-flowered; pedicel and ovary 5.2 – 6.8 mm long; sepals 3.5 mm long or less; lip 3.5 – 4.5 × 4.5 – 6 mm; spur 3.5 – 4 mm long...R. pareense

Discussion

Rhipidoglossum parense is endemic to Tanzania. It is only known from the floristic region Tanzania, T3, Kilimanjaro Region, Same District, Mwala Forest Reserve and from the Baga II Forest Reserve in the adjacent West Usambara mountains. With its limited range, occurring in a small area on only two mountains, it fits into the typical pattern of endemism exhibited by several plants recently described from the same region (Hemp 2015; Hemp & Crouch 2018) and various other biota in the Eastern Arc mountains (with flightless grasshoppers being a striking example (Hemp et al. 2015)), where about one third of the vascular plants are species of restricted range (Lovett 1998). This underscores the urgent need to conserve the remnant, highly fragmented forest patches in these mountains in the face of high anthropogenic landscape transformation (Newmark 1998).