Achyranthes acuminata E. Mey. ex Sonder

Sukhorukov, Alexander P., Kushunina, Maria, Nilova, Maya V., Baider, Cláudia & Sennikov, Alexander N., 2024, Africa and Arabia encompass a much greater species diversity in the Achyranthes aspera aggregate (Amaranthaceae, achyranthoid clade): Evidence from morphological and chorological data, PhytoKeys 250, pp. 21-94 : 21-94

Achyranthes acuminata E. Mey. ex Sonder , Linnaea 23: 96 (1850).

= Achyranthes aspera f. nigrescens Suess. , Bull. Jard. Bot. État Bruxelles 15: 56 (1938). Lectotype (designated here): DR Congo, [ Équateur Prov.,] Environs d’Eala , July 1930, J. Lebrun 1230 ( BR 0000008819543 !, isolectotypes BR 000000881923 !, K!).

– Achyranthes aspera var. rubrofusca auct. in herb. BM, K.

– Achyranthes bidentata var. africana Cavaco , nom. nud. in herb. BM, K.

– Achyranthes bidentata auct.: Baker and Clarke (1909), Hutchinson and Dalziel (1927), Keay (1954), Lebrun and Stork (1991), Figueiredo and Smith (2008), Phiri (2005), Klopper et al. (2006).

– Achyranthes africana Sukhor. , nom. nud. in herb. BM, BR, K.

Lectotype (designated here).

South Africa, Port Natal [Durban], schattige Waldplätze, 400 ft, 9 April 1832, Drège 4679 ( P 01029520 – image!).

Description.

(Figs 5 , 6 ). Annual or short-lived perennial herb up to 1.5 (2.0) m tall occasionally creeping and rooting at lower nodes; stem sparsely pubescent, obscurely quadrangular turning angular in the inflorescence; leaf petioles 10–40 (60) mm, blades 30–260 × 20–110 mm, cuneate, ovate or rhombic or even obovate, entire, tip short or long acuminate, deep green or olivascent and almost glabrous above, pale green or purplish and slightly to moderately pubescent below, usually turning blackish when dry; inflorescence 80–270 mm long, dense, paracladies always present, in early stages thin and delicate similar to inflorescences of some willows (e. g. Salix triandra ); bract 3.0–4.0 mm long; bracteoles (3.0) 4.0–5.0 mm long, reflexed; perianth segments slightly unequal, (4.5–5.0) 6.0–7.0 (8.0) mm long (two segments longer than three others), green outside and purple-red inside at least at the tip, turning dark brown when dry, three inner segments keeled; pseudostaminodes brownish (when dry), 0.8–1.1 mm, not or slightly fimbriate; stamens 5, filaments purple, anthers 0.35–0.6 mm long, magenta; style (1.3) 1.6–2.1 mm long, pink or mauve; fruit (without style) 1.7–2.5 mm long.

Taxonomic note.

For a long time, specimens of A. acuminata were identified as A. aspera or its varieties, e. g. A. aspera var. rubrofusca in the DR Congo, or as A. aspera var. nigrescens (Suessenguth in Suessenguth and Merxmüller 1951), and, in some cases in tropical Africa, as A. bidentata (e. g., Baker and Clarke 1909; Hutchinson and Dalziel 1927; Townsend 1973; Lebrun and Stork 1991; Klopper et al. 2006). Nonetheless, Townsend (1985) claimed that the Asian A. bidentata did not occur in East Tropical Africa and referred specimens of A. acuminata to A. aspera var. pubescens (Moq.) C. C. Towns. Lebrun and Stork (2003) vaguely discussed some morphological differences between A. aspera s. l. and A. bidentata from Asia and Africa, concluding that there are differences between both species as well as differences between Asian and African populations of A. bidentata .

Achyranthes acuminata differs from the Asian A. bidentata and A. japonica (Miq.) Nakai by its obovate leaves turning blackish when dry (facultative character) and longer (1.6–2.1 mm) styles. The two Asian species are rhizomatous perennial plants with ovate leaves, which do not turn black when dry, and have shorter styles (1.0– 1.5 mm long). To date, the presence of any species of the Asian A. bidentata group is not confirmed in Africa, and the native distribution of this group of species is restricted to tropical and warm temperate Asia (South and East China, Japan, South-East Asia, and countries located in the Himalayas). Achyranthes japonica is reported as an alien and naturalized plant in temperate North America ( Medley et al. 1985).

Achyranthes aspera var. rubrofusca was erroneously reported from Africa (Suessenguth in Suessenguth and Merxmüller 1951). Its basionym A. rubrofusca ( Wight 1852) was described from India and belongs to the A. bidentata group.

Nomenclatural notes.

The name A. acuminata was only mentioned (as nomen nudum) in Drège (1843), who cited a number of plant species (incl. A. acuminata ) growing in forests and woodlands (‘ Wälder und Holzungen’), and it was later validated by Sonder (1850). Cavaco (1962: 127) considered A. acuminata as a putative synonym of the subshrubby A. aspera var. porphyrostachya (≡ A. porphyrostachya ) probably based on similar leaf shape. Authentic specimens of A. acuminata have obovate leaves, different from A. porphyrostachya , which has oblong or ovate leaves. Moreover, A. acuminata and A. porphyrostachya can be separated based on their ecology.

An authentic specimen of A. acuminata kept at W ([without exact location and date] E. M. [eyer] (W 18393!) has a perianth shorter (4.5–5.0 mm long) than usual (6.0–7.0 mm). A shorter perianth length was also observed in specimens from dryer areas (e. g., growing in Ethiopia and Benin). On the other hand, the length of anthers (± 0.5 mm long) and style (± 1.8 mm) long is constant in the species.

Suessenguth (1938) cited two specimens of A. aspera f. nigrescens Suess. , which were collected in the Belgian Congo [now DR Congo]: Matadi [Kongo Central Prov.] and Eala [Équateur Prov.]. Both specimens represent the same species. Suessenguth was probably the first to mention its remarkable character: leaves turning black when dry.

Habitat.

Riverine and primary rain forests, forest margins and other wet shady places at elevations of 0–2000 m a. s. l.

Distribution.

(Fig. 7 ; see also Appendix 1). Africa: Angola, Benin, Botswana, Burundi, Cameroon, Central African Republic, Comoros, Congo Republic, DR Congo, Equatorial Guinea, Ethiopia, Gabon, Guinea, Ivory Coast, Kenya, Lesotho, Madagascar, Malawi, Mayotte, Mozambique, Namibia, Nigeria, Rwanda, São Tomé and Príncipe, Sierra Leone, Somalia, South Africa, Tanzania, Togo, Uganda, Zambia, Zimbabwe.

General distribution.

Tropical Africa.

Figures

Figure 5. Achyranthes acuminata A general view of the plants (Meru area, Arusha Region, Tanzania. Photographer: A. Sukhorukov) B close-up of the leaves and inflorescences (KwaZulu-Natal Province, near Durban, South Africa. Photographer: Errol Douwes).

Figure 6. A herbarium specimen of Achyranthes acuminata (Tanzania, Tanga Region, Gendagenda Forest, 200 m a. s. l., 31 Jul 1991, Frontier Tanzania team 2377, K).

Figure 7. Distribution map of Achyranthes acuminata.