Exochaenium clavatum Paiva and Nogueira, 1990

Kissling, Jonathan, 2015, Exochaenium clavatum subsp. stella-palustre (Gentianaceae-Exaceae), a new subspecies from Zambia, Phytotaxa 203 (3), pp. 297-300 : 298-299

Exochaenium clavatum Paiva and Nogueira subsp. stella-palustre Kissling subsp. nov. ( Figs. 1 and 2 )

Exochaenium clavatum subsp. stella-palustre differs from the typical subspecies by its smaller size (c. 20 cm tall) (vs> 30 cm tall); single-flowered inflorescence (vs at least 5 flowers per individual); calyx wing wider near the middle (vs wider near the base); basal leaves longer than cauline leaves (vs similar to the cauline leaves), massed at the base (vs leaves evenly spaced along the stem).

Type: — ZAMBIA. Kafwasa dambo, just S from the Chingola-Solwezi road, 1321 m, 12° 22’ 26.3 S, 27° 14’ 41.0 E, 14 April 2004, S. Dessein, R. Archer, P. De Block, J. Kissling, B. Luwingu & E. Tembo 934 (Holotype, NEU!; isotype, BR!) .

Description: –Annual, erect plants, up to 20 cm tall. Roots reddish. Stem simple, delicately winged. Leaves sessile opposite, massed at the base of the stem; blades linear-lanceolate, 10–20 x 1–2 mm, acute. Inflorescence single-flowered, subtended by 2, opposite, leaf-like bracts. Flowers 5-merous, erect, pedicellate (pedicels 13–15 cm long). Calyx lobes free, lanceolate, 8 mm long, winged dorsally, wings enlarged in its middle, up to 1 mm wide. Corolla bright yellow; tube infundibuliform, 10 mm long; lobes obovate, 4–5 mm long, apiculate. Filaments filiform, 1.5 mm long, inserted at the middle of the corolla tube; anthers oblong, 1 mm long, basifixed, included; apical gland conspicuous, ellipsoid; basal glands 2, minute. Ovary ovoid, 5 x 3 mm, bilocular, placenta axile, ovules numerous. Style filiform, included, 0.7 mm long; stigma slightly clavate, 2 mm long, papillose.

Etymology: –This taxon was found during a dark-cloudy day and its five yellow corolla lobes make it look like a star on the dark water background ( Fig. 2 ).

Distribution and ecology: –This subspecies is only known from the type locality in Zambia, where it was found growing in water in the center of a dambo (i.e. seasonally waterlogged, predominantly grass-covered, depressions bordering headwater drainage lines; Mackel 1985).

Suggested conservation status: –A first assessment results in “Data Deficient” because the extent of occurrence cannot be calculated with a single point. Nevertheless, several collections have been made in the last decades in Zambia and I have seen almost all collections of Exochaenium . Both subspecies seem to be rare and endemic to Zambia (see introduction). However, there is a small probability that E. clavatum subsp. stella-palustre might have been overlook due to its peculiar habitat (shallow water) and relative small size. I suggest the IUCN status endangered: B2a for this subspecies following IUCN (2001) criteria.

Figures

FIGURE 1. Exochaenium clavatum subsp. stella-palustre: Drawing of a whole individual measuring 20 cm. Drawn from S. Dessein, R. Archer, P. De Block, J. Kissling, B. Luwingu & E. Tembo 934 by Maeva Arnold.

FIGURE 2. Photograph of a flower of Exochaenium clavatum subsp. stella-palustre. Photo by J. Kissling.