Hemithrinax Hook.f., Gen. Pl. 3: 930 (1883)

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Number of Taxa

  • 3 species

Discussion

Biology And Ecology

Etymology

Diagnosis

Description

  • Small to moderate, solitary, unarmed, pleonanthic, hermaphroditic palms. Stem erect, sometimes very short, columnar, smooth or fibrous, sometimes obscured by a skirt of marcescent leaves, obscurely ringed with leaf scars, usually with a basal mass of fibrous roots. Leaves very crowded and congested or more laxly arranged, induplicate, palmate, often irregular; sheath becoming split both opposite the petiole and abaxially, sometimes scarcely fibrous, or disintegrating into irregular curled robust fibres, or fibres free proximally and united distally in a short or greatly elongated ligule-like structure, covered in thick, deciduous tomentum, margins fibrous; petiole very short to moderately elongate, slender, rounded to shallowly ridged both adaxially and abaxially, margins rather sharp; adaxial hastula prominent, triangular or rounded, abaxially hastula ridge-like, moderately conspicuous, rounded or triangular; blade fan-shaped, split to about half to two-thirds its length into single-fold segments, segments lanceolate, pointed and usually bifid apically, glabrous adaxially, sometimes densely covered in wax, abaxially variously scaly, sometimes white, midrib and marginal ribs conspicuous, abaxial surface of lamina with minute dot-like scales, transverse veinlets obscure. Inflorescences interfoliar, lax or congested, scarcely longer than the sheaths and protruding through the split petiole base, or erect, longer than the leaves, branched to 1–3 orders; peduncle rather slender, laterally compressed or rounded in cross-section; prophyll coriaceous, 2-keeled, with triangular tip, splitting apically and abaxially along its entire length (?always); peduncular bracts to 5 or apparently absent in Hemithrinax compacta, elongate, membranous or coriaceous, variously indumentose, with bifid tips, closely sheathing the peduncle and splitting only at the tip; rachis bracts 2 or 3 (H. rivularis, H. ekmaniana) or numerous to ca. 10 (H. compacta), spirally arranged, overlapping and very closely sheathing the rachis, each subtending a first-order branch, variously indumentose; first-order branches tapering, bearing spirally arranged bracts similar to but smaller than the rachis bracts, distally bearing minute triangular bracts subtending second-order branches or rachillae; rachillae slender, very short, much shorter or slightly longer than the rachis, glabrous or variously indumentose, stiff, bearing spirally arranged, small narrow triangular bracts subtending very small solitary flowers, bracteoles apparently lacking. Flowers sessile or borne on very short protuberances; perianth a single cupule with 6 triangular lobes; stamens 6–8, filaments short, basally connate in a ring, connective very broad, anthers oblong-elliptic in outline, dorsifixed and facing outwards at anthesis, forming a low ring around the gynoecium, extrorse; gynoecium consisting of 1 carpel, unilocular, uniovulate, conical, tapering into a short style, approximately twice as long as the androecium, stigma conduplicate, ovule basally attached, erect, campylotropous with a basal aril. Pollen ellipsoidal asymmetric, sometimes pyriform; aperture a distal sulcus; ectexine tectate, coarsely perforate and micro-channelled, wide psilate and sparsely perforate aperture margin; infratectum columellate; longest axis 24–26 µm. [1/3]. Fruit very small to moderate, white at maturity, stigmatic remains apical, perianth persistent; epicarp smooth when fresh, drying pebbled, mesocarp thin, mealy, endocarp very thin, papery. Seed depressed-globose, smooth or shallowly and sparsely grooved, hilum round, impressed, forming a basal intrusion, raphe branches sparse, shallowly impressed, endosperm homogeneous; embryo subapical. Germination not recorded; eophyll unknown. Cytology not studied. (J. Dransfield, N. Uhl, C. Asmussen, W.J. Baker, M. Harley and C. Lewis. 2008)

Relationships

Taxonomic accounts

Bibliography

  • Dransfield, J. , Uhl, N. , Asmussen, C. , Baker, W.J. , Harley, M. & Lewis, C. 2008. Genera Palmarum. The evolution and classification of palms. Kew Publishing, Royal Botanic Gardens Kew.