Rubiaceae of the New World

By Piero Delprete and Rocio Cortés
 

OSA Aiello

Osa pulcra                                     Photo L. Gilbert
Peninsula de Osa, Costa Rica

Small to medium-sized trees; raphides absent; axillary thorns absent. Stipules interpetiolar, connate at base, deltoid, acuminate, persistent. Leaves opposite, long-petiolate or short-petiolate; blades narrowly ovate or elliptic or oblong or narrowly oblong, chartaceous; foliar pellucid glands absent; domatia absent. Inflorescence axillary, uniflorous. Flowers bisexual, protandrous. Calyx tube absent, lobes free at base, persistent; lobes 5, linear, long, aestivation open. Calycophylls absent. Corolla trombiform, actinomorphic, white to cream-white, tube externally glabrous, internally glabrous, without a pubescent ring inside; orifice annular thickening absent; lobes 5, imbricate (tube reduplicate), broadly triangular, margin entire, obtuse at apex. Stamens alternate to the corolla lobes, partially exserted (only tips exserted); anthers long-linear, round at base, round at apex, dehiscing by longitudinal slits, basifixed; filaments attached at base of the corolla tube, basally connate (forming a minute tube at base of the corolla), slender, long, shorter than corolla tube, equal, glabrous. Pollen colpate, apertures 3, exine surface foveolate-perforate, released as monads. Style exserted just beyond the corolla, terete throughout, not fleshy, glabrous; lobes absent, stigmatic surface linear along style. Ovary inferior, 2-locular, obconical; placentation axile, placenta peltate to the entire lenght of the septum, ovules many per locule. Fruit a septicidal capsule, dehiscing basipetally, the valves not splitting at apex, thinly woody. Seeds descentingly imbricate, large, dorsoventrally compressed, elliptic to broadly elliptic in outline; wings absent.

Geographic distribution: Southern Central America. Endemic to the Peninsula de Osa, Costa Rica.

Number of species: 1.

References: A. Aiello, A reexamination of Portlandia (Rubiaceae) and associated taxa. J. Arnold Arb. 60: 38–123. 1979.