Baphia arenicola Goyder, F.M.P. Goncalves & P.Meller, 2023

Goyder, David J., Davies, Nina, Finckh, Manfred, Gomes, Amandio, Goncalves, Francisco Maiato P., Meller, Paulina & Paton, Alan J., 2023, New species of Asclepias (Apocynaceae), Baphia (Leguminosae), Cochlospermum (Bixaceae) and Endostemon (Lamiaceae) from the Kalahari sands of Angola and NW Zambia, with one new combination in Vangueria (Rubiaceae), PhytoKeys 232, pp. 145-166 : 145

Baphia arenicola Goyder, F.M.P. Goncalves & P.Meller sp. nov.

Diagnosis.

Most similar morphologically to B. massaiensis Taub., from which it can be readily distinguished by its geoxylic lifeform, flowering and fruiting at ground level on short, prostrate above-ground shoots, and the villous suture of the keel petal.

Type.

Angola. Moxico Province: tributary of the Lungue-Bungo River 42 km SSE of Munhango, 12°31'34"S, 018°40'13"E, fl. 22 October 2016, D.Goyder & F.Maiato 8772 (holotype: K (K001333933); isotypes: INBAC, LUBA) .

Description.

Geoxylic suffrutex forming large patches; above-ground shoots prostrate, 5-10 cm long, pubescent, arising from extensive woody below-ground stems. Leaves unifoliolate; stipules linear, 3-4 mm long, densely pubescent with silvery hairs; petiole 3-5 mm long, pulvinus barely apparent; leaflet narrowly obovate-oblong and generally folded along the midvein, 4-6 cm long, 1-2 cm wide, obtuse apically, tapering somewhat towards the base, ± glabrous except for the major veins beneath. Inflorescences with an indumentum of greyish or golden hairs; flowers 1-3 in sessile or subsessile axillary fascicles; pedicels 15-20 mm long; bracteoles 1-2 mm below the calyx, caducous. Calyx 7-10 mm long, spathaceous. Petals white, the standard with a yellow triangular mark towards the base; standard 10-12 × 8-10 mm, emarginate; wings c. 10 × 2 mm; keel 10-12 × 2.5-3 mm, lower suture villous distally. Stamens 10, free. Ovary 6-9 mm long, villous, with a glabrous upturned style. Legume c. 7 cm long, c. 1.5 cm wide, brown. Seeds c. 10 mm long, dark brown or black. (Figs 5 , 6 ).

Distribution and ecology.

Flowering in October and November in the late dry season or at the onset of the rains; fruiting in February. Known from three sites, the first in the Lungué-Bungo river system of western Moxico Province at an elevation of around 1350 m, the second in the Cusseque River system of Bié Province some 200 km to the SW of the Moxico site at around 1530 m, and the third just over the watershed into the Cacuchi River valley which drains into the Rio Cuchi and is around 1540 m. The three sites are similar topographically, with broad fossil river terraces and sandy alluvial deposits rich in geoxylic suffrutices ( Gröngröft et al. 2013b, Revermann et al. 2013, Goyder et al. 2018). (Map 4 ).

Conservation status.

Baphia arenicola is known from three localities, two of which have vouchered herbarium collections. TFO project made many unvouchered observations of the plant in the Cusseque and Cacuchi River valleys and it is clear that there are extensive populations of this species. There are no significant threats to these nutrient-poor grasslands rich in geoxylic suffrutices as the environment is not conducive to agricultural development. B. arenicola is therefore provisionally assessed as Least Concern.

Additional specimens examined.

Angola. Bié Province: Cusseque, TFO core site relevé 23324, 13°41'53"S, 017°06'43"E, fl. 29 October 2011, Finckh 132753 (HBG, K); Cusseque, TFO core site relevé 23349, 13°41'53"S, 017°07'48"E, fl. 2 November 2011, Revermann 132895 (HBG, K); Cusseque village , Chitembo, 13°43'21"S, 017°05'53"E, fr. 17 February 2014, Gomes & Maiato 161 (LUBA); Cusseque 15 September 2019, Finckh 145383A (HBG, LUBA); Cusseque, 28 January 2020, Finckh 145352B (HBG, LUBA) .

Taxonomic notes.

Baphia Afzel. ex G.Lodd is a genus of around 50 species of woody legumes which has diversified across tropical Africa ( Soladoye 1985, Goncharov et al. 2011). A single species extends its distribution to the white sands of NW Madagascar, with a second species endemic to that region ( Stirton and Du Puy 1992). Members of the genus are recognised readily by their unifoliolate leaves, free rather than united stamens, and flat, dark brown seeds lacking an aril. Seeds of other genera of the unifoliolate Baphioid clade of Lewis et al. (2005) are globose, arillate, and bicoloured or otherwise brightly coloured ( Cheek et al. 2014). Baphia species occur in evergreen forest, thicket and woodland with several species restricted to white sands ( Stirton and Du Puy 1992, Brummitt 2007, Mackinder and Clark 2012, Cheek et al. 2014). While most species are shrubs or small trees, B. aurivellerea Taub. from NE Angola and western DR Congo can be suffrutescent, but this species still possesses erect woody shoots 20 cm to two metres above ground level. In contrast, an undescribed species encountered in central Angola flowers at ground level on short, prostrate above-ground shoots and is here formally described as Baphia arenicola .

Most floral characters invite comparison with the locally common woodland species B. massaiensis , with its spathaceous calyx split longitudinally down a single line, bracteoles longer than wide and positioned shortly below the apex of the pedicel, glabrous staminal filaments, and pubescent ovary. The keel petal which is somewhat villous along its line of fusion, however, suggests links to B. bequaertii De Wild., another miombo woodland species of the region. Preliminary molecular analyses by one of us (PM) places the new taxon close to the latter species, with estimated divergence times from B. bequaertii less than 1 mya. Divergence times from B. massaiensis , on the other hand, are estimated to be between 11 and 27 mya.

Figures

Map 4. Known distribution of Baphia arenicola (central Angola).

Figure 5. Baphia arenicola A habit B bud C open flower D standard petal E wing petal F keel petal G androecium H stamen J gynoecium K fruit. Drawn by Margaret Tebbs from Goyder & Maiato 8772 (flowering material) and Gomes & Maiato 161 (fruit).

Figure 6. Baphia arenicola. Photographed by David Goyder at the type locality.