Acanthonema (in its traditional sense)

Acanthonema (in its traditional sense)

Full name and orig. publication: Acanthonema Hook.f., Bot. Mag. t. 5339 (1 Oct. 1862).

Etymology: From the Greek άκανθα, acanthos = spine, thorn, and νημα, nēma = thread, alluding to the anterior stamens which possess a tooth-like process at the apex.

Synonym: Carolofritschia Engl. (1899).

Infrafamilial position: Didymocarpoid Gesneriaceae - "African and Madagascan genera" (Weber 2004).

Description: Monocarpic unifoliate herbs. Stem short, with fibrous roots at base, bearing a single hairy leaf (macrocotyledon) of variable (usually oblong-cordate) shape and size. Cymes several- to many-flowered, shortly pedunculate, emerging in a series from the leaf base, bracteoles small. Sepals free to base, linear-oblong. Corolla infundibuliform, white with bluish lobes; tube curved, slightly inflated towards the mouth; limb subregular, lobes short, rounded. Stamens 4, included, usually only 2 (the anterior pair) fertile; filaments adnate to middle of corolla tube, somewhat thickened and flattened in the middle, those of the anterior pair with a tooth-like process at the apex; anthers with divaricate, apically confluent thecae, cohering face to face. Nectary unilateral, bipartite, oblique, nearly half as long as ovary. Ovary conical, bilocular, with axile placentae, the recurved lamellae ovuliferous all over; style c. 4x as long as ovary; stigma shortly bifid. Fruit ovoid-conical, not twisted, mode of dehiscence unknown (simply breaking with age?). Seeds reticulate (Beaufort-Murphy 1982).

Chromosome number: Unknown.

Species number: 2.

Species names: A. diandrum (Engl.) B.L.Burtt, A. strigosum Hook.f.

Type species: Acanthonema strigosum Hook.f.

Distribution: Tropical W Africa (S Nigeria, Fernando Po, Cameroun, Gabon).

Ecology: Growing on humid rocks or rocky river banks in forest, partly also epiphytic on the base of moss-covered trees (Burtt 1963).

Notes: In habit the genus superficially matches a unifoliate Streptocarpus. Apart from the disjunct distribution, there are significant differences in the reproductive characters: (a) flattened, toothed filaments, (b) unilateral nectary, (c) short, ovoid fruit.

Selected references: Burtt, in Hutch. & Dalz., Fl. West Trop. Africa, ed. 2, 2: 383 (1963); Burtt, Bull. Mus. Nat. Hist. Nat. B., Adansonia 3: 415-417 (1982), inclusion of Carolofritschia; Burtt, Fl. Cameroun 27: 16-21 (1984), reg. rev.; Burtt, Fl. Gabon 27: 10-15 (1985), reg. rev.; Weigend & Edwards, Bot. Jahrb. Syst. 118: 59-80 (1996), palyn.

Tax. details, cytology, and bibliography: Gesneriaceae Resource Centre (GRC). Royal Botanic Garden Edinburgh.

Page content and update responsibility/contact: Anton Weber.
Because of the synonymisation of Acanthonema, this page is no longer updated.