Exallosperma De Block, 2018

Block, Petra De, Rakotonasolo, Franck, Ntore, Salvator, Sylvain G. Razafimandimbison, & Janssens, Steven, 2018, Four new endemic genera of Rubiaceae (Pavetteae) from Madagascar represent multiple radiations into drylands, PhytoKeys 99, pp. 1-66 : 1

Exallosperma De Block gen. nov.

Diagnosis.

Unique within the tribe Pavetteae by the pollen with psilate tectum and by the fruit containing 2 stony pyrenes, each with a laterally flattened ovoid seed with irregularly distributed surface ridges formed by elongation of the exotesta cells.

Type species.

Exallosperma longiflora De Block.

Shrubs, with Terminalia -branching pattern, branching modules consisting of a long-shoot, horizontal in orientation, never bearing inflorescences and relatively smooth, and an inflorescence-bearing short-shoot with short internodes, erect in orientation, densely beset with corky stipular remnants and alternating vegetative and reproductive nodes; vegetative parts pubescent. Leaves grouped terminally on short-shoots, deciduous, petiolate with petioles long, slender and canaliculate above; blades papyraceous; hair tuft domatia present; margins not revolute; bases rounded, subcordate, cordate or unequal, more rarely truncate or obtuse. Stipules keeled, with a dense row of large colleters interspaced with hairs at the base but otherwise glabrous on the inner surface except for the tip, dimorphic: in vegetative nodes consisting of truncate or triangular sheaths forming a cone and topped by needle-like awns, in inflorescence-bearing nodes consisting of ovate sheaths with acute or shortly acuminate tips. Inflorescences seemingly terminal but actually pseudo-axillary on erect short-shoots, pedunculate, pauciflorous, cymose with trichotomous branching; all parts (axes, bracts, bracteoles, pedicels) pubescent; bracts and bracteoles well-developed, linear. Flowers hermaphroditic, pentamerous, shortly pedicellate; all parts (ovary, calyx, corolla) pubescent outside; secondary pollen presentation present. Calyx well-developed; tube short; lobes much longer than tube. Corolla white, turning yellowish with age; tube narrowly cylindrical; lobes contorted to the left in bud and spreading at anthesis. Stamens sessile, inserted in the sinuses of the corolla lobes somewhat below the level of the throat; anthers almost completely included in the corolla tube at anthesis, basimedifixed, with sagittate base and short sterile apical appendix. Disc annular, fleshy, glabrous. Ovary cup-shaped, bilocular; placentation axile, with 3-4 ovules arising on top of a small placenta attached to the base of the septum. Style and stigma only just exserted from the corolla tube at anthesis; stigmatic lobes slender, fused over their entire length except for the very tips, receptive zone on the adaxial surfaces of the free tips and along the lines of fusion of the lobes. Fruits drupaceous, ovoid, pubescent, crowned by the persistent calyx, containing 2 pyrenes; pyrene stony, hemi-ellipsoid with the abaxial side convex and the adaxial side consisting of a flat rim but otherwise open (with the openings of the two pyrenes inside a fruit separated by the membraneous septum), with a short apical longitudinal preformed germination slit on both abaxial and adaxial sides, containing 1 seed; seed laterally flattened, ± bean-shaped; hilum superficial, irregularly ovate, moderate annulus around hilum present; seed surface not smooth but with irregularly distributed ridges formed by the seed-coat; exotesta cells with continuous plate-like thickenings along the outer tangential and upper parts of the radial walls, irregular ridges on seed surface formed by strongly elongated exotesta cells; endotesta consisting of crushed cell layers with many crystals; endosperm entire. Pollen grains 3-zonocolporate, exine psilate, supratectal elements absent.

A monospecific genus, endemic to northern Madagascar, occurring on calcareous soil.

Etymology.

This genus is named for its peculiar seeds.