Rustia occidentalis (Benth.) Hemsl.

Authority

Delprete, Piero G. 1999. Rondeletieae (Rubiaceae). Part I. Fl. Neotrop. Monogr. 77: 1-226. (Published by NYBG Press)

Family

Rubiaceae

Scientific Name

Rustia occidentalis (Benth.) Hemsl.

Type

Type. Colombia. Narino: Isla Gorgona, 1841 (fl), Hinds 354 (lectotype, K, selected by Delprete, 1999b; isolectotype, BM).

Description

Species Description - Shrub 2-5 m tall, exceptionally a tree to 8 m tall, to 30 cm dbh, much-branched, rarely single-stemmed; bark grayish. Leafy branchlets glabrous, dark green, terete; older branches rugose, grayish; lenticels many, punctiform to linear, 0.5-4 mm long. Stipules narrowly triangular, acuminate, glabrous outside, glabrous with basal colleters inside, 10-15(-30) × 2530 mm, dark green, readily caducous, leaving a white-grayish linear scar. Leaves 17-28(-40) × 4-12 cm, L/W 2.5:1 to 4:1; narrowly elliptic, lanceolate to oblanceolate, cuneate to acute (BA = 18-25°) at base, acute-caudate at apex, tapering to a long acuminate apex, the acumen often falcate, 1.5-3 cm long; dark green above, pale green below, foliaceous; drying grayish olive-green, stiff-chartaceous; glabrous above and below; pellucid punctate; primary and secondary veins glabrous, slightly depressed above, prominent below, secondary veins 11-16 each side; tertiary veins starting subparallel and reticulate in the center; petioles 20-40 mm long, 1-2.5 mm thick, adaxially concave to flattened; pulvinus evident in young leaves, becoming corky in mature leaves; domatia absent. Inflorescences reduced-paniculate to racemoid, opposite to subopposite decussate lateral branches; 4-11(-15) × 2-10(-13) cm, lateral branches to 4 pairs, basal portion of axis not branched to 3 cm long; rachis decussately compressed to terete, rachis and branches glabrous; flowers alternate on distal branches or in sparse cymules; distal bracts 1-2 × ca. 1 mm, deltoid; bracteoles subtending flowers ca. 1 × 0.7-1 mm, deltoid, glabrous. Flowers pedicellate, pedicels 4-15 mm long, glabrous; hypanthium narrowly turbinate, 3-5 × 2-3 mm, glabrous; flower buds clavate. Calyx reduced to an undulate margin, to 3 mm long, sometimes ciliolate. Corolla tubular, medially faintly constricted with perpendicularly spreading lobes, 1.1-1.4 cm long, purple to flesh-red outside, white to pearl-white inside, carnose to coriaceous when fresh; tube subcylindrical, 7-9 mm long, 2.5-3.5 mm wide at base and 4-5 mm wide at the orifice, glabrous outside, glabrous inside, without ring of hairs; lobes 5 (rarely 4), 1/2 of corolla length, 5-6 × 1.7-2 mm, triangular, glabrous outside and inside. Stamens 5, exserted because of spreading lobes, subequal, attached 4-5 mm from the base of the tube; filaments ca. 2 mm long, glabrous, distally terete, basally flattened-adnate to tube, ca. 0.8 mm at base; anthers convex toward the center, yellow, banana-shaped, 5-7 × 1.8-2 mm, dorsifixed near the base, base rounded, smooth throughout. Pollen exine reticulate. Style exserted, 10-14 mm long, glabrous; style branches ovate, 0.8-1.2 × ca. 0.9 mm, stigmatic surface smooth. Capsules obovoid to widely obovoid (rarely globular), obtuse to rounded at base, apex hemispherical, 7-12 × 7-9 mm, dark brown to black at maturity, with minute lenticels, glabrous throughout; disk septicidal dehiscence present of old capsules. Seeds 1.06-1.26 × 0.67-0.83 mm.

Discussion

Bentham (1844) first described this species as Exostemma (sect. Pseudostemma) occidentale from specimens collected from the Gorgona Island, near the Pacific coast of Colombia. In his protologue Bentham did not refer to specific collections, but nevertheless one herbarium specimen preserved at Kew bears the label: "Exostemma occidentale Benth., Voy. Sulph. 104, a large shrub, Isle Gorgona, Hinds 1841." This is probably one of the specimens that Bentham saw when he described the species, and I selected this as lectotype (Delprete, 1999b). Hemsley (1881) later transferred it to Rustia, citing three specimens: "Guatemala (Friedrichstal); Panama (Fendler 289); Colombia Hb. Kew." The last specimen is probably the one seen by Bentham when he described this species.

Pollination:I observed Rustia occidentalis in coastal swampy sites of Choco, Colombia, where in some areas this species is in almost pure stands. The flowers of this species are fleshy and purple-red to flesh-red, and never pendulous. Rustia occidentalis is mainly visited by bees (Euglossa sp. and Melipona sp.; see Fig. 23C,D), which perform a rather characteristic buzz-pollination. During late-morning hours, if one listens carefully in a large population of this species, it is possible to hear the scattered buzzing of bees visiting the flowers. This is the first species of the entire Rubiaceae that has been observed and reported to be buzz-pollinated.

Distribution

Mostly in swampy coastal areas (Fig. 23A), near the coast but not influenced by salt water, in proximity of streams in lowland costal forests, and in coastal areas of some islands, 0-300 m, in Nicaragua, Guatemala, Costa Rica, Panama, Colombia, and N Ecuador. Flowering specimens were collected in all months of the year except January. Fruiting specimens were collected in February, March, April, July, August, and December.

Guatemala Central America| Izabal Guatemala Central America| Nicaragua Central America| Zelaya Nicaragua Central America| Costa Rica South America| Cocos Island Costa Rica Central America| Limón Costa Rica Central America| Puntarenas Costa Rica Central America| Bocas del Toro Panamá Central America| Colón Panama Central America| Darién Panamá Central America| Chocó Colombia South America| Nariño Colombia South America| Valle Colombia South America| Ecuador South America| Esmeraldas Ecuador South America|