Aptosimum spinescens (Thunb.) Emil Weber

Kolberg H., van Salgeren M. 2016. A synopsis of Aptosimum and Peliostomum (Scrophulariaceae) in Namibia, including the description of a new species, Aptosimum radiatum, and keys to all accepted species. Kew Bulletin 71:16. DOI 10.1007/S12225-016-9628-7

Type

Type: locality not indicated [but in view of its publication assumed to be from South Africa, Western Cape Prov., Cape of Good Hope], Thunberg s.n. (lectotype UPS-THUNB, selected here; isolectotype LD-1242485!).

Morphology General Habit

Shrub, erect, spinescent, 15 – 30 (– 60) cm tall

Morphology Stem

Stems decumbent-ascending, much- to sparsely branched, woody, 5 – 8 mm diam., glabrous, scabrid with stiff hairs to glandular-pubescent, hairy mostly below leaf insertion, may be densely leafy or bear short, leafy shoots; bark whitish, corky, to 2 mm thick

Morphology Leaves

Leaves alternate to clustered, subulate, linear-oblanceolate to spathulate, 6 – 30 × 1 – 4 mm, glabrous to densely antrorse scabrid, may be folded along midrib and arched downward; apex acute, spiny; base cuneate, sessile; midrib prominent beneath, pale, sometimes scabrid at base, spinescent; spines numerous, strong, to 1 mm wide at base, mostly straight; margins stiff bristly

Morphology Reproductive morphology Flowers

Flowers solitary or in 3-flowered dichasia, in upper axils, sessile to subsessile, usually overtopping leaves; bracteoles linear, 3 – 5 mm long

Morphology Reproductive morphology Flowers Calyx

Calyx lobed to middle at most, tubular to campanulate, 5 – 10 mm long, densely glandular-pubescent or puberulous outside and inside; tube 2 – 7 × 3 – 5 mm; lobes filiform, lanceolate, triangular or ovate, somewhat unequal, 2 – 5 × 1 – 2 mm, long ciliate in sinuses and sometimes on margins, apex acuminate and glabrous

Morphology Reproductive morphology Flowers Corolla

Corolla 12 – 20 mm long, shortly glandular outside; tube basally narrow, 6 – 8 × 1.5 mm, widening upwards to 5 mm diam., curved or with indistinct bulge on abaxial side, mouth oblique, whitish to pale lilac with dark venation outside; lobes orbicular to obovate, 2 – 5 mm long and wide, inside lilac to pale purple, dark purple patch at base

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens four, unequal; filaments with membranous margin, base stipitate-glandular, longer pair 5 – 6 mm long, shorter pair c. 4 mm long; anthers almost equal in size, ciliate-bristly

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary pubescent, sometimes with sessile glands; nectary shallowly cup-shaped; style filiform, to 12 mm long, equal in length to corolla; stigma indistinctly emarginate or capitellate

Morphology Reproductive morphology Fruits

Capsule ovoid, obovoid or globose, 5 – 8 × 4 – 6 mm, shorter than calyx, short hairy to densely glandular-hairy or glabrous; apex cordate, somewhat or abruptly compressed

Morphology Reproductive morphology Seeds

Seeds elongate to reniform, 1.5 × 1 mm, black, scrobiculate to tuberculate; funicle thickened

Distribution

Africa: Namibia, South Africa.

Ecology

Occurs in various soil types, including sand and loam; calcrete and dolomite are the most common lithology. Found on plains, in dry river beds and drainage channels, on hill and mountain slopes, in depressions and pans of the shrubland, escarpment and inselbergs, desert, desert – dwarf shrub savanna transition, dwarf shrub savanna, Kalahari sands, dwarf shrub savanna – Kalahari sands transition and succulent steppe vegetation types (Mendelsohn et al. 2010). Recorded in the Welwitschia Desert, Highlands to 1500 and 1800 m, Escarpment, Southern Namib Succulent Desert, Huns-Orange and Gordonia phytogeographical groups (Craven 2009). Altitude: 250 – 2000 m.

Conservation

Aptosimum spinescens is widespread in Namibia and occurs in large populations. The EOO and AOO under criterion B are well above thresholds for the threatened categories (IUCN 2012, 2013) and no threats were identified, thus resulting in an evaluation of LC. The status in South Africa is also LC (SANBI 2014).

Phenology

Flowering and fruiting throughout the year. Peak flowering: Feb. – March. Peak fruiting: March – May.

Vernacular

Doringviooltjie, rolvarkie (Afrikaans, South Africa).

Note

Thunberg’s specimen in UPS-THUNB is selected here as lectotype for Aptosimum spinescens being from the describing author’s herbarium. Drège s.n. (P-3411726) is selected as the lectotype for A. abietinum, being a more copious specimen compared to the other syntypes and with Drège’s handwritten locality on it. Schenck 59 is selected as the lectotype for A. scaberrimum, Fleck 542 is selected as the lectotype of A. scaberrimum var. glabrum, Rehmann 3239 is selected as the lectotype for A. scaberrimum var. tenuifolium, and Steingröver 17 is selected as the lectotype for A. steingroeveri since none of the other syntypes for the respective names could be traced at herbaria where specimens of those collectors are normally housed. The specimen of Dinter 4854 at B is selected here as lectotype of A. laricinum because it is a good quality specimen with a label in Dinter’s handwriting and from the herbarium where the collector’s first set of specimens are housed. None of the syntypes of A. steingroeveri var. glabrum could be found. Merxmüller & Roessler (1967) already treated A. steingroeveri and A. steingroeveri var. glabrum as synonyms of A. spinescens but their publication does not indicate if they had seen the types. From the description of A. steingroeveri var. glabrum we do, however, agree with them.

As can be deduced from the number of synonyms for this species and its wide distribution, it is highly variable (Figs 15 & 16), but Merxmüller & Roessler (1967: 19) found that it is impossible to clearly separate this complex into species or even at the infraspecific level. The supposedly differentiating characters overlap and differences in, for instance, leaf width are not correlated with characters like indumentum, plant habit or distribution.

The variability of what is presently considered to be Aptosimum spinescens also includes A. neglectum Emil Weber. A. neglectum was initially listed by Bentham (1836) as A. abietinum var. elongatum (“elongata”) based on a Drège specimen with a locality “on the Gariep”, locality III B 11 according to Drège (1843). He did not provide a description and this is therefore a nomen nudum. In his description of A. neglectum, Weber (1903: 895) included A. abietinum var. elongatum as a synonym, but he based his description on the type specimen only (Drège s.n. [2443], P-3411723, possible duplicate P-3411729). Weber admitted in his treatment of the genus (1907: 29) that he did not see any of the specimens listed by Hiern (1904) for var. elongatum (Shaw 1240 and Muskett in Herb. Bolus 6481), thus implying some doubt about var. elongatum being synonymous with A. abietinum. Hiern (1904) noted that there were intermediate forms between A. abietinum and A. abietinum var. elongatum. All this would support a sinking of A. neglectum into A. abietinum. Weber (1907) included A. abietinum (var. abietinum) in A. spinescens, a concept followed by subsequent authors. A. spinescens is highly variable and its present circumscription would include A. neglectum. In the online specimen database of the South African National Biodiversity Institute there are no specimens of A. neglectum, possibly because it is indistinguishable from A. spinescens. More detailed study than is merited within this synopsis is necessary, especially of South African specimens of A. neglectum (including at least its type specimen) and A. spinescens, to clarify whether they are indeed synonymous.