Craterostigma loitense I.Darbysh. & Eb.Fisch., 2017

Darbyshire, Iain & Fischer, Eberhard, 2017, A new species of Craterostigma (Linderniaceae) from Kenya, Phytotaxa 306 (1), pp. 91-95 : 92-94

Craterostigma loitense I.Darbysh. & Eb.Fisch. sp. nov. ( Fig. 1 )

Lindernia sp. A (“loitensis”) sensu Agnew (2013: 300, pl. 115).

Type: — KENYA. Loita Hills, Enkang Sapuk Camp, on ridge above Entesakerra, 2300 m, 20 June 2009, A.D. Q. Agnew & J. Agnew s.n. (holotype EA 000004205!).

Craterostigma loitense differs from C. purpureum in the leaf margin subentire to minutely serrate (vs. entire), in the two abaxial staminodes with minute rudimentary anthers (vs. fertile), and in the anthers of the fertile stamens with basal tuft of long hairs (vs. hairs lacking).

Subrosulate dwarf annual herb, leaves clustered between very short internodes, sometimes with a longer trailing internode 11 mm long between leaf clusters. Stems 4-angular, puberulous, hairs blunt-tipped. Leaves subsessile or with flattened petiole to 3 mm long; blade somewhat fleshy, adaxial surface green, abaxial surface often purple, at least towards apex, ovate to narrowly so or elliptic, 6.5–11 × 2.5–4.7 mm, base attenuate, margin subentire or minutely serrate, apex narrowed into an acute or blunt tip; midrib prominent, lateral veins inconspicuous; young leaves minutely puberulous, later glabrescent. Inflorescences axillary with flowers usually held well above the leaf rosettes; flowers solitary, ebracteolate; pedicels 4–12 mm long or rarely shorter in flower, extending to 11–22 mm long in fruit, indumentum as stems. Calyx green with purple lobes or purple extending to near the base, 3.0– 4.5 mm long in flower, extending to 4–5 mm long in fruit, shortly and unevenly 5-lobed, longest (adaxial) lobe 1.0– 2.2 mm long, shortest (abaxial) pair of lobes 0.4–1.25 mm long, sparsely puberulous mainly along midrib of each lobe and towards lobe apices. Corolla white with purple streaking on the limb, bilabiate; tube held erect, cylindrical, 3.0– 3.3 mm long, c. 1.5 mm in diameter; lips 3.0– 3.4 mm long when flattened; upper lip hooded, triangular-attenuate from broad base, 3.0– 3.4 mm wide at base, apex shortly bilobed; lower lip with three rounded lobes 1.5–1.7 mm long with irregular margin, palate minutely puberulous centrally and extending into throat. Stamens two, adaxial, attached at base of upper lip, filaments 0.7–1.1 mm long, convergent, the divergent anther thecae forming a cross-shape, thecae 0.6–0.7 mm long, lower theca of each stamen with a basal tuft of long hairs; staminodes two, abaxial, attached on palate of lower lip, geniculate with a swollen yellow-puberulous boss and a recurved filament together up to 1.5 mm long when flattened, apex with a vestigial anther up to 0.25 mm long. Pistil glabrous; ovary oblong, ± 2 mm long; style slender, ± 2 mm long; stigma of two broad membranous lobes, ± 0.75 mm in diameter; disc annular but with one side incomplete. Capsule elongate, (5.0–) 8.5–12.0 × 1.5–2.5 mm, glabrous; seeds ± 0.5 × 0.4 mm, bothrospermous, with longitudinal ribs and finer transverse ribs.

Distribution: —Southern Kenya (Flora of Tropical East Africa region K6), only known from the type locality.

Etymology: —Named after the type locality of the Loita Hills.

Habitat and Ecology: —Shallow soils on quartzitic rocks at 2300 m elevation, growing under the edges of tall plants. The species is reported as poikilohydric ( Agnew 2013).

Conservation status: — Craterostigma loitense is only known from the type collection. The area where it occurs is grazed and trampled, which may help to maintain the open habitat the plants require, although the substrate is so nutrient-poor that this may also limit dense woody growth (A.D.Q. Agnew, pers. comm.). As the specimens of C. loitense are so tiny, they could easily be overlooked and may well occur at other sites in the Loita Hills and beyond. In the light of the limited distribution, population and threat data on this species, it is provisionally assessed as DD (Data Deficient), following the Categories and Criteria of IUCN (2012).

Taxonomic notes: — Craterostigma loitense appears from morphological evidence to be most closely allied to C. purpureum from the Democratic Republic of the Congo. However, it clearly differs in having the combination of a subentire to minutely serrate leaf margin, the two abaxial staminodes having minute rudimentary anthers and in the anthers of the fertile stamens having a basal tuft of long hairs, whilst in C. purpureum , the leaves are entire, the abaxial stamens are fertile and the anthers are glabrous. Within its range, it superficially resembles Linderniella pulchella (Skan in Hemsley & Skan 1906: 348) Fischer et al. (2013: 227) in general habit and leaf shape, but differs in the truncate inflorescence with single long-pedicelled flowers in the axils of the basal rosulate leaves while L. pulchella has a main stem with a racemose inflorescence bearing bracts with axillary flowers above the basal rosulate leaves. Furthermore the abaxial staminodes lack any anther vestiges in L. pulchella , and the fertile anthers lack the basal tuft of hairs. The only other African Linderniaceae bearing a tuft of hairs at the base of the anthers are Craterostigma engler i and C. gossweileri from Angola and C. yaundense from Cameroon, all growing on granitic rock outcrops. They share with C. loitense the basal rosulate leaves and the lack of a main inflorescence, but all three differ from it in the axillary inflorescence always having a distinct long peduncle bearing bracts with axillary flowers, the corolla being bluish, and the sterile abaxial staminodes being geniculate or clavate and lacking an anther vestige ( Fischer 1992).

Additional specimens examined: —Hort. A.D.Q. Agnew, August–September 2010, A.D.Q. Agnew s.n. (EA!).

Craterostigma purpureum Lebrun & Toussaint in Robyns (1943: 83) —D.R. CONGO. Parc National de Virunga , May ya moto, savane au bord de la Rutshuru, July 1937, Lebrun 6919 (holotype BR!); plaine de la Rusizi, region de Luberizi, Mt. Kalambo , 24 February 1950, Germain 6280 ( BR!) ; plaine de la Rusizi, Bulamata, March 1950, Germain 663 ( BR!) .

Figures

FIGURE 1.—Craterostigma loitense. A–D: habit, A & D in flower, B & C in fruit; E & F: dissected corollas; G: calyx dissected to show pistil; H & I: abaxial staminodes with vestigial anthers; K: detail of fertile anther from adaxial stamen. Drawn by E. Fischer, A from photograph of living material, B–K from the holotype (A.D.Q. Agnew & J. Agnew s.n.).