Octolepis, Oliv.

Rogers, Zachary S., 2005, A revision of Octolepis Oliv. (Thymelaeaceae, Octolepidoideae), Adansonia (3) 27 (1), pp. 89-111 : 91-93

OCTOLEPIS Oliv.

J. Linn. Soc. Bot. 8: 161, t. 12 (1865).

Makokoa Baill., Bull. Mens. Soc. Linn. Paris 1: 619

(1886). — Type: Makokoa congolana Baill.

TYPE. — Octolepis casearia Oliv.

Shrubs or trees; plants monoecious (Africa) or dioecious ( Madagascar); bark longitudinally striate, sometimes lenticellate. Leaves alternate or opposite, often discolorous, caducous or persistent on mature stems, estipulate; leaf blades glabrous adaxially, sparsely covered with inconspicuous adpressed indument abaxially or glabrescent (trichomes c. 0.5-1 mm long), margin entire, ± revolute; midrib grooved adaxially, raised abaxially; venation brochidodromous; fine venation reticulate; leaf buds conduplicately folded, covered with dense indument; petioles grooved adaxially, articulate, drying darker than midrib. Inflorescences axillary and fasciculate (Malagasy species), or lateral (or sublateral) and borne on short woody compact racemose axes (African species); inflorescence bracts absent; pedicels articulate. Flowers white, small, bisexual or unisexual; staminate and pistillate flowers of similar size and shape; floral tube absent; sepals 4-6, imbricate, reflexed or spreading, rarely erect, persistent in fruit; petals scale-like, 4 or 5 (10), bifid, divided nearly to base, adnate to receptacle, persistent in fruit; stamens twice the number of petals, (8) 10 (12) (20), straight in bud, ± inserted in a single whorl, persistent in fruit; anthers oblong, introrse, basifixed. Staminate flowers with a minute pistillode; pistillode obscured by many erect receptacle trichomes. Pistillate flowers with (8) 10 (12) (20) persistent staminodes; rudimentary anthers globose or undifferentiated; subgynoecial disc absent; gynoecium 3-6-carpellate, sessile; carpels uniovulate; ovary superior, usually one to several locules aborting, densely pubescent, surrounded by many erect receptacle trichomes; ovules minute, anatropous, pendulous; style terminal, straight, persistent; stigma globose, lobed, papilliate. Fruits green-yellow or white ( O. casearia ), loculicidal capsules, subspheroidal to ovoid-pyramidal, developed carpels producing longitudinal lines of dehiscence; dehiscence lines depressed or ± plane, often bicarinate on both sides of line; pericarp dry and thin, or fleshy and thicker. Seeds brown or black, ovoid, triangular or circular in cross section, edges rounded, adaxial side often costate, curved, abaxial side costate, other sides curved or ± flat; seed coat crustaceous, thin, outer epidermis puberulent, indument red-orange, denser near poles, inner epidermis finely striate; endosperm copious; cotyledons longitudinally curved, thin (c. 0.5-1.5 mm thick).

INFRAGENERIC CLASSIFICATION OF OCTOLEPIS

Octolepis casearia , the continental African species, differs significantly from the Malagasy taxa by a number of vegetative, floral, and fruit characters ( Table 1). The petals of O. casearia ( Fig. 1A, B ) have an obvious papilliate surface sculpturing. In O. dioica ( Fig. 1C ), the petals are also papilliate, but the sculpture pattern is rarely evident because of the dense indument covering the lobes. Petal indument in O. casearia is always tomentose or tomentose-strigose, usually concentrated along the margin and apex of the lobes, and the trichomes are not oriented in a particular direction. The petal indument of O. dioica is representative of the other Malagasy species and is characterized as strigose (never tomentose) on both surfaces with the individual trichomes always oriented toward the receptacle (receptacle located just outside the bottom of the frame in Figure 1C ). Populations of African and Malagasy Octolepis are separated geographically by c. 3000 km.

In addition to the substantial morphological and geographical differences, these two groups form distinct monophyletic lineages. Combined rbc L and trn- F sequence data taken from the five recognized Malagasy species, both varieties of O. casearia , and a sample of O. decalepis (sensu Gilg), indicate that each group is monophyletic with 99% bootstrap support (WURDACK unpubl. data).

Based on these strong lines of supporting evidence, the following infrageneric classification for Octolepis is proposed, to stress the significant differences between these two groups. Two sections are recognized here: sect. Octolepis (the sole continental African species, O. casearia ) and sect. Dioicae Z.S.Rogers (the five Malagasy species).

Figures

FIG. 1. — SEM microphotograph of the petals in Octolepis: A, O. casearia (sect. Octolepis), adaxial surface of sepals (S) and abaxial surface of petal lobes (L). The arrow indicates the point where two erect lobes meet to form a single deeply divid- ed bifid petal. The stamens located just above petal lobes are out of frame; B, papilliate abaxial surface of the petal shown in A at higher magnification; C, O. dioica (sect. Dioicae), adaxial surface of a bifid petal. A, B, Breteler et al. 9450, WAG pickled sample; C, Razakamalala 748, MO pickled sample.