Inversodicraea xanderi Cheek, 2017

Tchouto, P. & Burgt, X. van der, 2017, A synoptic revision of Inversodicraea (Podostemaceae), Blumea 62 (2), pp. 125-156 : 147-148

26. Inversodicraea xanderi Cheek , sp. nov. — Fig. 5

With Inversodicraea harrisii C.Cusset , I. congolana Hauman and I. tenax (C.H.Wright) Engl. , unusual in the genus in having projections from the abaxial surface of the leaflet (not flat, as in all other species). Most similar to I. tenax in having multiple projections, but differing from all three species in having 5 or more marginal teeth, not tridentate, and in the strongly dimorphic scale-leaves,those on the stem distant from the spathellae having (6–)7–9 teeth and lacking abaxial projections (not tridentate with abaxial projections). — Type: van der Burgt 1940 (holotype K; isotypes P, YA n.v., Z), Cameroon, South Region, Campo, Campo-Ma’an National Park, North of the road Campo to Ma’an, N2°20'57.1" E10°13'21.8", old fr., alt. 230 m, 4 Mar. 2016.

Etymology. Named for Xander van der Burgt (1958–) Dutch botanist, formerly of the Herbarium Vadense, Wageningen, now of the Royal Botanic Garden, Kew, specialist in field surveys in tropical Africa, and especially in the Leguminosae­Caesalpinoideae. Collector of the only known specimen of Inversodicraea xanderi .

Erect annual herb, 1.5–3 cm tall including fruits ( Fig. 5b ). Root horizontal, dorsiventrally flattened (ribbon-like), adhering to substrate, 1.5–2 mm wide, lateral branches arising at 50–60° from the main axis, at intervals of 6–8 mm; internodes 1–5 mm long ( Fig. 5a ). Stems erect, terete, leaflet-clad, 0.1–1.6 cm long, 0.4–0.6 mm diam, 0.7–0.8 mm wide including scale-leaves. Leaves not seen, probably caducous, dichotomously branched. Scale­leaves completely covering the stems, appressed, dimorphic: a) normal scale-leaves ( Fig. 5e ) 1–1.6 by 0.7 mm, distal part hemi-orbicular, digitately (6–)7–9-toothed, teeth marginal, subequal, narrowly conical, length: breadth c. 2–3: 1, length 0.1–0.2 mm; b) distal scale-leaves ( Fig. 5d ), subtending spathellae, 1–1.1 by 0.7 mm, free, distal part oblong to triangular, marginal teeth 5–6, each (0.1–) 0.2–0.3 mm long, abaxial surface with (4–)5–7(–10) conical projections, each 0.05–0.3 mm long. Spathellae single, terminal or subterminal. Pedicel 12–14 mm long in fruit. Gynophore with distal 0.9–1.1 mm decorticating, leaving only the 6 vascular strands ( Fig 5c 2 ). Tepals, androecium and ovary unrecorded. Fruit narrowly cylindric-ellipsoid, c. 2.5 by 0.4–0.5 mm, with 6 longitudinal ribs, ribs conspicuous, subequal ( Fig. 5c 2 ); sutures not pronounced (commissural ribs absent), dehiscing by two sutures, valves not caducous. Seeds unrecorded.

Distribution — Cameroon, South Region, Campo.

Habitat & Ecology — On rocks in stream 0–50 cm above water level near Campo town in primary evergreen forest; 230 m altitude.

Conservation — Known only from one location on the river near Campo inside the Campo-Ma’an National Park currently one of the most protected areas in Cameroon. The AOO is estimated as 1 km 2. It is here assessed as NT in view of the small AOO, since no threats are currently known. Should threats be evidenced, this species should be reassessed as Critically Endangered.

Additional specimens. CAMEROON, South Region , Campo , Campo-Ma’an National Park , North of the road Campo to Ma’an, N2°20'57.1" E10°13'21.8", old fr., alt. 230 m, 4 Mar. 2016, van der Burgt 1940 (holotype K; isotypes P, YA n.v., Z) .

Notes — Decortication of the outer surface of the developing fruit exposes the longitudinal ribs of Inversodicraea according to Thiv et al. (2009). In I. xanderi this same process appears to extend from the base of the fruit to the gynophore, leaving the first connected to the pedicel only by the six vascular strands that comprise the fruit ribs ( Fig. 5c 2 ). The annual nature of I. xanderi is confirmed by the type material, all of which appears to have been dead before it was collected.

The abaxial leaflet projections are conjectured to aid the protection of the developing spathellae from predation by grazing animals.

Inversodicraea xanderi is known from a post-mature, fruiting collection. In the shape and toothing of the majority of its scale-leaves it is similar to I. cristata , which also occurs in Cameroon. It is likely that the two have an affinity. The points of separation between the two species are detailed in Table 1. The abaxial projections of the spathellae-subtending scale-leaves of I. xanderi are rarely encountered in Africa, being seen in only three other species, all of which differ from I. xanderi in numerous points (see above, under ‘diagnosis’). Flowering material of this taxon is desirable.

Figures

Fig. 5 Inversodicraea xanderi Cheek. a. Root viewed from above, showing erect leaflet covered stems and pedicel bases; b. erect, sparingly branched stem with fruits; c1. detail of fruiting stems, with c2 detail of dehisced fruits; d. detail of spathellae-subtending scale-leaves; e. detail of normal scale-leaves (all from Xander van der Burgt 1940, K). — Scale bars: a–b = 1 cm; c1–c2 = 2 mm; d–e = 1 mm. — Drawn by Andrew Brown.

Fig. 2 Inversodicraea feika Cheek. a. Habit in dry season; a1. branched, erect flowering plant, leaves fallen; a2. subcylindrical root developing from old stem; b1. detail of a1; b2. detail of spur shoot with scale-leaves; c. stolon-like root upper surface, showing opposite, distichous short leaves and endogenous branch- ing; d. stolon-like root, lower surface, with two undifferentiated endogenous root branches (detail from a2); e. spur shoot with spathellum just after dehiscence; f. spur shoot, with flower at anthesis; g. fruit; h. fruit in transverse section, three seeds in lateral view above (all from Feika 78B, K). — Scale bars: a = 1 cm; b–d = 5 mm; e–g = 2 mm; h, b (small inset) = 0.5 mm. — Drawn by Andrew Brown.