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Streptocarpus Lindl. [family GESNERIACEAE]

Date Updated: 26 July 2007

Herbarium
Royal Botanic Gardens, Kew (K)
Collection
Flora Zambesiaca
Resource Type
Reference Sources
Entry From
FZ, Vol 8, Part 3, page 43, (1988) Author: O. M. Hilliard and B. L. Burtt
Names
Streptocarpus Lindl. [family GESNERIACEAE], in Bot. Reg. 14 tab. 1173 (1828).—Hilliard & Burtt, Streptocarpus: An African Plant Study (1971).
Information
Herbs, rarely subshrubs; caulescent, erect or creeping, or acaulescent, rosulate or unifoliate; annual, perennial or monocarpic. Leaves opposite and petiolate in the caulescent species (very rarely alternate and sessile, and then the flowering axis with a very large basal leaf); in the acaulescent species the leaf may show continued growth from a basal meristem, evidenced by wide-spreading lateral veins and frequent absence of intact apex; indumentum of simple glandular or eglandular hairs, rarely of branched hairs; sessile or subsessile glands usually present: the lower surface of the leaf sometimes white-dotted due to the presence of stomatal turrets. Inflorescences axillary or apparently from base of lamina or from leaf-stalk; cymose, branching, sometimes more or less one-sided, the flowers paired, rarely reduced to two flowers or only one. Calyx usually divided to the base into 5 segments, more rarely with a distinct tube and 5 teeth. Corolla gamopetalous, 5-lobed, most often distinctly bilabiate. Stamens arising at various levels on the corolla tube, the anterior 2 only fertile; lateral staminodes usually present, the posterior one often missing; filaments variable in length, often thickened in the middle; anthers with divaricate, rarely parallel, lobes, the lines of dehiscence confluent at the apex, usually cohering face to face. Disk annular or shortly cupular. Ovary usually unilocular, but sometimes apparently bilocular by fusion of the T-shaped intrusive placentae; ovules restricted to the recurved tips of the placentae; ovary narrowed, often very gradually, into the style; stigma variable. Capsule more or less cylindrical, varying from short and broad (5 mm.) to long and slender (180 mm.), twisting spirally before maturity, dehiscing by a loculicidal slit and slight untwisting of the spiral, when old sometimes splitting into 4 valves. Seeds numerous, small, with very little endosperm, reticulate or verruculose. Seedlings with the cotyledons becoming unequal after germination.
Range
A genus of about 135 species in Africa, Madagascar and E. Asia, but the four Asiatic species are doubtfully congeneric.
Notes
Streptocarpus is divisible into two subgenera: subgen. Streptocarpus comprising acaulescent species (there are a few exceptions), which develop an abscission layer towards the base of the lamina during the unfavourable season and have the peduncles arising from the base of the lamina or from the petiolode; and subgen. Streptocarpella K. Fritsch, comprising caulescent species, which lack radical leaves; the cauline leaves have no abscission layer and the peduncles are axillary. The subgenera are also separated by a difference in chromosome number: 2n = 32 in subgen. Streptocarpus, 2n = 30 in subgen. Streptocarpella. subgen. Streptocarpella is represented in the area of Flora Zambesiaca only by S. buchananii; all the other species in this area belong to subgen Streptocarpus and are strictly acaulescent with the exception of S. myoporoides.In a revision of the whole genus (Hilliard & Burtt 1971) an aggregate species concept was employed where necessary to give a loose linkage between very closely allied species whose reduction to subspecific rank would scarcely have been warranted and would have led to an unnecessarily cumbersome nomenclature.Two such aggregate species are represented in the Flora Zambesiaca area. S. agg. cooperi (based on the Natal species S. cooperi C.B.Cl.) includes from our area S. grandis, S. michelmorei and S. solenanthus; S. agg. monophyllus (based on the Angolan S. monophyllus Welw.) includes S. eylesii, S. wittei and S. arcuatus.This aggregate species concept is not included in the formal presentation of the Flora account, but it is as well to remind the user that it has been found necessary. In some cases the component species of these aggregates may not be easy to distinguish.The occurrence of wild hybrids may be a source of difficulty in naming specimens, particularly in the eastern highlands of Zimbabwe and in adjoining Mozambique (see Hilliard & Burtt 1971, pp. 91–92). Hybrids are likely both within and between the two aggregate species mentioned above; otherwise S. umtaliensis is the only species that is at all likely to be involved and the evidence here is very slight. Individual instances are mentioned under the species concerned. It can only be emphasised that when a plant or population seems to vary from the typical form of its species an attempt to relate this to characters of other species present in the area is always worth while.
Streptocarpus Lindl. [family GESNERIACEAE]
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