Dichapetalum petaloideum Breteler, 2005

Breteler, F. J., 2005, Novitates Gabonenses 53. A curious new species of Dichapetalum (Dichapetalaceae) from Gabon, Adansonia (3) 27 (2), pp. 231-234 : 231-234

Dichapetalum petaloideum Breteler , sp. nov.

Dichapetali crassifolii Chodat optime affine de folio inflorescentiaque, sed singulatim in genere petalis indivisis crassis valvatis et pilosis.

TYPUS. — Wieringa & van Nek 3284, Gabon , Echira, ± 2° 3 ’S, 9°48’E, alt. ± 30 m, fl. 25 Nov. 1994 (holo-, WAG; iso-, BR, C, G, K, LBV, LISC, MA, MO, MPU, NY, P, UPS, US) .

Liana at least 12 m long. Branches and branchlets with a pale-grey, powdery indumentum, glabrescent with age. Stipules early caducous, triangular, 3-4 mm long, c. 2 mm wide, tomentellous outside, ± glabrous inside. Leaves: petiole subterete, grooved above, 7-14 mm long, indumentum as on branchlets; lamina coriaceous, shiny, obovate to oblong-elliptic, 2- 2.5 times as long as wide, (8-)9-15(-17) × (2-)4-7(-8) cm, cuneate to rounded and sometimes unequal-sided at base, acute to shortly acuminate at apex, the acumen subacute, <5 mm long; midrib and the 5-8 pairs of main lateral nerves ± plane above, prominent beneath; leaf surface glabrous both sides except for the extension of the petiole indumentum on the midrib, especially so beneath; glands ± small, ± well dispersed, mainly on the lower surface.

Inflorescence glomerate to very shortly (up to 5 mm) pedunculate, sometimes arranged on short, leafless, axillary shoots, up to 2 times distinctly branched, up to c. 25-flowered, with a powdery to tomentellous indumentum; bracts and bracteoles ± broadly triangular-ovate, acute, up to 1 mm long, tomentellous; pedicels 1-2 mm long, articulated at or near the apex; sepals palegreen, imbricate, ± stiff, erect, slightly concave, shortly united at base, ovate-triangular, 3-3.5 × 2 mm, tomentellous outside as well as on the upper part inside; petals white to cream-coloured, entire, firm, valvate in bud, at base laterally united with the alternating filaments in a c. 1 mm long tube, ± flat, lanceolate, 3-4 × 1 mm, the free parts tomentellous outside as well as on the apical part inside; stamens c. 2 mm long, the filaments white, almost completely adnate to the adjacent petals, glabrous; anthers c. 1 mm long, ± ovoid in outline; staminodes (disc glands) subquadrate, ± flat, c. 0.3 × 0.3 mm, glabrous; pistil 1.5-2 mm long; ovary depressed globose, 3-locular, velutinous-tomentellous; style white, glabrous, c. 1 mm long, 3-lobed apically. Fruits unknown. — Fig. 1.

HABITAT AND DISTRIBUTION. — Rain forest in

SW Gabon. Only known from the type locality .

DISCUSSION. —The indumentum of the petals of African Dichapetalum species varies from completely absent or with only a few hairs just below the lobes outside, which is quite common, to hairy on the upper part outside (e.g., D. reticulatum Engl. , D. trichocephalum Breteler ) to pubescent both sides (e.g., D. pierrei Pellegr. , D. rudatisii Engl. ). In all these instances, however, the petals are thin, and, as a rule, bilobed and bicucculate. They never show characteristics like those of D. petaloideum , which are firm, entire, ± flat and lanceolate in outline. By its vegetative parts and its inflorescence the new species resembles D. crassifolium Chodat very much. The latter has also entire or nearly entire petals, but they are thin and ± glabrous.

Although of staminodial nature, like all the petals in Dichapetalaceae ( BRETELER 1973: 25) , those of D. petaloideum seem to function like true petals in showing protective aspects ( Fig. 1D ), hence its epithet petaloideum : having a floral envelope resembling petals. The flower tube looks like a true corolla tube with the filaments adnate to it. However, it is composed of 10 elements, five petals and five filaments, the latter filling the gaps between the former ( Fig. 1H, I ).

To identify D. petaloideum with BRETELER’ s (1986) Key II: Central African Species (p. 22) it seems best to make use of its aberrant characters. Preceding couplet 1 add a new couplet 0 as follows:

— Petals firm, entire, lanceolate, ± flat .................................................................................... D. petaloideum — Petals thin, as a rule bilobed and bicucculate apically .................................................................................. 1

For the Flore du Gabon ( BRETELER 1991: 30) the same preceding couplet is proposed:

— Pétales fermes, entiers, lancéolés, ± plans ............................................................................ D. petaloideum — Pétales minces, habituellement bilobés et bicucculés au sommet .................................................................. 1

N OT E S. — On my request Dr W. P U N T investigated the pollen of D. petaloideum . His conclusion (pers. comm.) is that the pollen of this species shows advanced characteristics as of the D. heudelotii -group in the D. heudelotii - type ( PUNT 1975). According to PUNT the pollen does not show any character which indicates that another classification for this species, e.g., in a separate, new genus, might be justified.

Cuts of the branches of the holotype show some traces of an exudate as seen in D. crassifolium Chodat ( BRETELER 1978: photograph 3).

Boiling flower material of D. petaloideum soon rendered the water reddish brown. The same happened to the alcohol (60%) in which this boiled material was preserved.

Figures

FIG. 1. — Dichapetalum petaloideum Breteler: A, flowering branch; B, apex of branchlet (b) with inflorescence in leaf axil (p, petiole) showing stipules (s); C, leaf axil with inflorescence; D, flower bud; E, open flower; F, sepal inside; G, flower cut lengthwise; H, flower tube from outside; I, flower tube from inside; J, pistil. Wieringa & van Nek 3284. Drawing by H. DE VRIES.