Gretheria Duno & Torke, 2022

Tamayo-Cen, Ivan, Torke, Benjamin M., Lopez Contreras, Jose Enrique, Carnevali Fernandez-Concha, German, Ramirez Morillo, Ivon, Can Itza, Lilia Lorena & Duno de Stefano, Rodrigo, 2022, Revisiting the phylogeny and taxonomy of the Pithecellobium clade (Leguminosae, Caesalpinioideae) with new generic circumscriptions, PhytoKeys 205, pp. 279-298 : 279

Gretheria Duno & Torke gen. nov.

Diagnosis.

Similar to Havardia in arboreal or shrubby habit, vegetative branches arising both proleptically and sylleptically, leaves microphyllous, inflorescence arising on long shoots, pod flattened-compressed and seed plumply disciform to orbicular, but differing in the pinnae distally accrescent (vs. decrescent at each end in Havardia ), the calyx longer and deeply campanulate (vs. shorter, and shallowly campanulate), and the corolla lobes erect-ascending at anthesis (vs. recurved).

Type.

Gretheria sonorae (S. Watson) Duno & Torke.

Description.

Xerophytic, microphyllous arborescent shrubs and small trees, 2-14 m tall, commonly armed with stout recurved, lignescent stipules on the trunk and at each node of long-shoots, indumented with minute whitish trichomes on new growth. Leaves bipinnate, with 1-6 (13) pairs of pinnae; leaflets 10-31 per pinna; principal leaf axis typically 2-15 cm long, with the petiole 2-24 mm long, bearing a nectary at or below the mid-point of the petiole, the nectary sessile, shallow-cupular, thick-rimmed or plane and dimpled, pinnae axes sometimes with similar but smaller nectaries between 1-2 (3) distal-most pinna pairs and a minute one at the tip of some pinna-rachises; leaflets opposite, the blade oblong-elliptic to linear-oblong, subcordate at base, obtuse or shortly apiculate at apex; pilosulous or glabrous and marginally ciliolate; venation pinnate, immersed above, prominulous beneath, the mid-rib slightly displaced, giving rise on each side to 2-5 weak secondary veins expiring submarginally or faintly brochidodromous. Inflorescence capituliform racemes arising from leaf axils of long shoots and coeval with or preceding the leaf and/or arising from brachyblasts; peduncles (1.3) 2 cm long; capitula 10-37-flowered, receptacle clavate, 1.5-2.5 mm diameter; bracts ovate, minute, less than 1 mm long, sessile, persistent into anthesis. Flowers sessile, homomorphic, the perianth 5-merous; calyx deeply campanulate, glabrous, teeth deltate-ovate, ciliolate and sometimes distally puberulent or strigose; corolla subcylindrical, lobes erect, white-silky strigose dorsally; androecium 40-52-merous, 9-13 mm long, tube 3.6-5 mm long, nectar disc simple callosities or 5-lobed, 0.2 - 0.35 mm tall; ovary subsessile, slenderly ellipsoid, stipe 0.1-0.25 mm long; style about as long as stamens, the stigma poriform. Pods 1-3 per capitulum, oblong in profile, contracted at base into a pseudostipe ± 5-14 mm long and abruptly so at apex into an erect cusp 1.5-8 mm long; body straight or almost straight, 6.5-13 × (1.3) 1.2-2.4 (2.6) cm, plano-compressed, the valves bluntly framed by longitudinally 3-ridged sutures ± 1.5-2 mm wide, stiff, somewhat brittle, brownish-green, externally veinless, glabrous, red-granular or both granular and puberulent outside, the cavity continuous; funicle dilated, sigmoid. Seeds transverse, 8-13, plumply disciform to orbicular in outline, 9-12 × 7-10 mm, the pleurogram U-shaped.

Geographic distribution.

Gretheria comprises two species in United States (Texas), Mexico and Central America (Honduras and Nicaragua).

Habitat.

Gretheria grows in tropical deciduous dry forests, thorn scrubs and brush-woodlands, between sea level and 400 m elevation, occasionally ascending to 700 m.

Etymology.

The generic name honours Rosaura Grether González, an extraordinary and prolific Mexican botanist, with whom we had the pleasure of sharing her experience as a botanist and colleague. Her profound dedication and perseverant commitment to botanical research over decades has contributed importantly to our knowledge and understanding of Leguminosae, especially of the genus Mimosa L.