Inversodicraea ebo Cheek, 2017

Tchouto, P. & Burgt, X. van der, 2017, A synoptic revision of Inversodicraea (Podostemaceae), Blumea 62 (2), pp. 125-156 : 145-147

25. Inversodicraea ebo Cheek , sp. nov. — Fig. 4

Differs from I. cristata Engl. in having wings extending from the distal parts the non-commissural ribs of the ovary (vs wings absent), in having the base of the stem with either scattered, non-pectinate scales or (next to the substrate) naked, with a corky epidermis (in I. cristata the stem is covered in pectinate scales to the base),and in the leaflet lobes being nearly parallel-sided with an abruptly rounded apex (not narrowly triangular with an acute apex). — Type: van der Burgt 1716 (holotype YA; isotype K), Cameroon, Littoral Region, Yabassi, Ebo proposed National Park, near Locndeng, Ebo River , fl., 7 Dec. 2013.

Etymology. Named for the Ebo River and Ebo proposed National Park to which this species is unique according to the evidence available.

Rheophytic, probably perennial herb. Basal thalloid portion thick, orbicular, 1.5–1.6 cm diam, margin shallowly lobed, upper surface entirely lacking leaves but with a single tree or shrub-like stem arising from the centre ( Fig. 4a ). Stem erect, robust, 0.6–0.8 cm diam at base, unbranched for (0.6–) 1–2 cm, then dividing into 2–3 subequal branches, those branches themselves dividing every 1–2 cm along their length, and the resultant branches further, until c. 50 stem apices are present; stem apices 1.5–2 mm diam, 80–100 % clothed in pectinate scale-leaves ( Fig. 4f ); stems equidistant between apex and base becoming wider, 1.8–2.2 mm diam, 40–50 % covered by scale-leaves; stems 1–3 cm above the base 2.2–3 mm diam, the scale-leaves lacking their pectinate margin; stem bases, at junction with thalloid area, lacking scale-leaves, surface with grey-brown corky isodiametric cells 0.003 mm diam ( Fig. 4b , inset detail). Scale­leaves appressed, flattened, orbicular-oblong in outline (0.75–)0.85–1.2(–1.3) by (0.4–) 0.5– 1.2 mm, the proximal, entire part crescent-shaped, its distal margin extending into 8–14 subequal, subparallel, linear divisions 0.3–0.5 by 0.05(–0.1) mm, apices acute, the shorter divisions marginal, leaflet attachment curved, 0.3–0.75 mm long. ( Fig. 4g ). Leaves arising terminally on stems, stems then dividing into two, so that the leaves appear to arise in the axils of dichotomous stem forks ( Fig. 4b ); proximal 1/2–2/3 (1.7–2.1 cm) of leaf entire, ribbon-like in transverse section c. 1.5 by 0.5 mm; distal 1/2–1/3 branching dichotomously up to 5–7 times, with 27–70 terminal filiform segments c. 1.5–2 by 0.05 mm, stipules absent ( Fig. 4c ). Spathellae single or in pairs at stem apex ( Fig. 4f ); buds cylindric-ellipsoid c. 2 by 1 mm, mucro 0.25 mm long, apex truncate-rounded, base sessile, concealed by scale-leaves; opening by an irregular tear into two parts, pedicel c. 3.5 mm long at anthesis. Tepals filiform, 0.5–1.1 mm long inserted opposite to the androecium 0.1–0.3 mm below the insertion of the gynophore. Androecium slightly longer than the ovary (2.2–2.5 mm long), stamens two, free filaments 0.8–0.9 mm long, anthers 0.65–0.7 by 0.3–0.4 mm. Pollen in monads, prolate, 54–69 by 38 µm. Ovary ellipsoidoblong, slightly laterally flattened, the median and submedian nerves of each valve extended distally into rounded-triangular, fin-like wings, 0.15–0.2 by 0.2–0.35 mm; united to each other distally; gynophore 0.15–0.3 mm long; stigmas irregularly swollen, subcylindrical, tapering gradually to apex, 0.9 by 0.15 mm. Capsule hexagonal in transverse section, 0.8 by 0.6 mm ( Fig. 4k ) with 6 major and 2 minor (commissural) longitudinal, convex ribs ( Fig. 4k ). Seeds ellipsoid 0.3 by 0.15 mm.

Distribution — Cameroon endemic, known only from the Ebo River near Locndeng in Littoral Region.

Habitat & Ecology — Rheophyte on rocks in rapids of river.

Conservation — Known only from the type location in the Ebo proposed National Park to which this species is unique according to the evidence available. Threats include forest clearance for oil palm plantations, logging, and open cast iron ore mining, any of which would result in increased surface run-off and increased turbidity of the water which forms the habitat for this species. The AOO is estimated as 1 km 2. Accordingly, I. ebo is here assessed as Critically Endangered, CR B2 ab(iii).

Notes — Inversodicrea ebo appears to have a close affinity to both I. cristata and I. tchoutoi . All three species resemble miniature, highly branched, bonsai trees. All three have the broad, convex apex of the leaflet divided often into ten or more subequal regular divisions. While in the last species these divisions are equilaterally triangular, those in the two former are long and slender. However, I. cristata and I. ebo are separated by the characters given in the diagnosis. The distally winged ovary ribs of I. ebo are unusual in the genus, otherwise occurring only in I. warmingiana , I. eladii , and I. congolana .

The robust construction of I. ebo suggests that it is a long-lived, perennial species. It is conjectured that the scale-leaves near the base of the stem lack pectinate margins due to age, and that the corky base of the stem is an adaptation to guard against desiccation in the drier season when the plants are exposed above waterlevel.

Figures

Fig. 4 Inversodicraea ebo Cheek. a. Habit, whole plant in flower and fruit, showing disc-like thalloid portion anchored to rock; b. details of non-flowering plant, showing (below) base of stem (inset detail of corky epidermal cells) and non-pectinate scale-leaves on branches; (above) terminal origin of leaves (inset transverse section of leaf base); c. detail of dichotomously branched leaves; d. portion of lower stem showing scale-leaves lacking pectinate margins; e. stem from midpoint of plant showing pectinate scale-leaves covering c. 50 % of surface; f. stem apex with spathellae buds and scale-leaves covering 80–100 % of surface; g. three scale-leaves showing variation (dotted basal line indicates insertion on stem); h. flower emerging from spathellum, before anthesis; i. flower detail at anthesis, note the distally united wings of the ovary ribs; j. whole flower at anthesis, including spathellum; k. fertilised ovary, transverse section, slightly laterally flattened; l. seed, side view (all from Xander van der Burgt 1716, K). — Scale bars: a = 5 cm; b = 1 cm; c–f = 2 mm; g–j = 1 mm; k–l = 500 µm. — Drawn by Andrew Brown.