Asclepias minutissima Goyder, 2023

Goyder, David J., Davies, Nina, Finckh, Manfred, Gomes, Amandio, Goncalves, Francisco Maiato P., Meller, Paulina & Paton, Alan J., 2023, New species of Asclepias (Apocynaceae), Baphia (Leguminosae), Cochlospermum (Bixaceae) and Endostemon (Lamiaceae) from the Kalahari sands of Angola and NW Zambia, with one new combination in Vangueria (Rubiaceae), PhytoKeys 232, pp. 145-166 : 145

Asclepias minutissima Goyder sp. nov.

Diagnosis.

Asclepias minutissima appears most similar to A. aurea (Schltr.) Schltr. but differs in the campanulate rather than rotate to reflexed corolla, the ascending disposition of the corona rather than radiating from the column in A. aurea , the absence of the well-developed distal tongue to the corona of the latter species, and the shorter peduncles (1-3 cm rather than (3)5-14 cm in A. aurea ).

Type.

Angola. Moxico Province: Mussuma plains, 50 km NE of Lumbala, Zambezi drainage, 13°45'49"S, 021°43'25"E, fl. 7 December 2019, D.Goyder & F.Maiato 9204 (holotype: K (K001334259); isotypes: INBAC, LUBA, PRE) .

Description.

Perennial herb with a single erect stem arising annually from a small napiform tuber, latex white; stems 8-15 cm long, minutely pubescent along two lines. Leaves sessile, 3-7 × 0.05 cm, filiform with inrolled margins, glabrous. Inflorescences terminal or extra-axillary, umbelliform, with 4-5 erect flowers; peduncles 1-3 cm long, minutely pubescent; pedicels c. 1 cm long, minutely pubescent. Sepals 1-1.5 mm long, narrowly to broadly triangular, glabrous. Corolla campanulate, lobes 3.5-4 × 1.5 mm, oblong, green or white, glabrous on both faces. Corona lobes 2-3 mm long, cucullate, lacking an apical tongue, pinkish cream or white. Anther wings 1 mm long. Stylar head flat. Follicles not seen. (Fig. 1 ).

Distribution and ecology.

Known from a single collection in eastern Angola and one in NW Zambia. The Angolan population consisted of several scattered individuals on a broad open sandy plain just above the water table. Both the Angolan and the Zambian localities are on Kalahari sand deposits, and the Angolan collection was associated with common geoxylic suffrutices of the region such as Parinari capensis Harv., Syzygium guineense (Willd.) DC. subsp. huillense (Hiern) F.White, Eugenia malangensis (O.Hoffm.) Nied., Lannea gossweileri Exell & Mendonca subsp. gossweileri and Cryptosepalum sp. aff. mimosoides Welw. ex Oliv. Altitude 1100-1300 m. (Map 1 ).

Conservation status.

Asclepias minutissima is known from two localities some 350 km apart, but is inconspicuous and easily overlooked and is likely to be more common than the herbarium records suggest. Both localities are in nutrient-deficient sandy environments unsuitable for agriculture, and with little threat of habitat transformation as human settlements are few and far between. The new species is therefore provisionally assessed as Data Deficient.

Additional specimens examined.

Zambia. Mwinilunga District , 16 km along road from Matonchi Farm, 11°39'S, 24°03'E, fl. 17 November 1962, Richards 17269 (K) .

Taxonomic notes.

Only three species of Asclepias were reported from Angola by Goyder (2008). Asclepias baumii Schltr., known only from the type collection which was destroyed in Berlin, is almost certainly synonymous with A. aurea , as is A. radiata S.Moore ( Goyder 2009). Asclepias randii S.Moore is also present. Following the transfer of Odontostelma Rendle to Asclepias by Goyder (2009), A. minor (S.Moore) Goyder, also occurs in the country. All of these species occur in scattered populations with few individuals, as is common for Asclepias and allied genera in tropical Africa. As a result, they tend to be collected very infrequently and few herbarium records exist for any of them in Angola.

Asclepias randii is a much more robust plant than the other species and has pubescent stems and leaves. A. aurea and A. minor are glabrous and are slender herbs. Asclepias minor has a corona which is much reduced, not even reaching the base of the anther wings and has a short ventral appendage. So the species most similar to our new collection appears to be the highly variable A. aurea , which occurs across Namibia, southern Angola, Zambia, the Katanga region of the D.R.Congo, Zimbabwe, northern provinces of South Africa, Eswatini (Swaziland) and Lesotho ( Goyder 2009).

Asclepias aurea has rotate to reflexed corolla lobes, corona lobes which radiate from the column and are extended into a long distal tongue, and longer peduncles. In addition to the rather subtle morphological characters that distinguish the new species from A. aurea , its ecological requirements, close to the water table on leached Kalahari sand, are probably also significant. Asclepias aurea occurs on richer soils. The new taxon was mentioned by Goyder et al. (2020: 276) in a note under the related A. aurea but the Angolan (type) collection was cited incorrectly as Goyder & Gonçalves 4809.

Figures

Figure 1. Asclepias minutissima A habit B flower C corona lobe D gynostegium E pollinarium. Drawn by Margaret Tebbs from Richards 17269.

Map 1. Known distribution of Asclepias minutissima (eastern Angola and NW Zambia).