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

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Distribution

Map uses TDWG level 3 distributions (https://github.com/tdwg/wgsrpd)
Cuba present (World Checklist of Arecaceae)B
Three species, all very local endemics in Cuba (Muñiz and Borhidi 1982, Borhidi and Muñiz 1985). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Discussion

  • These remain rather poorly known palms, not often cultivated. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Diagnosis

  • Small to moderate, solitary hermaphroditic fan palms endemic to Cuba; leaf sheaths fibrous, petiole bases deeply split at base; fruit very small, white, the seed smooth or shallowly grooved. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Biology And Ecology

  • Found only on limestone outcrops (Hemithrinax compacta and H. ekmaniana) up to about 400 m elevation and on ultramafic soils near streams at low elevation (H. rivularis). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Etymology

  • Combining hemi — half, with the palm generic name Thrinax, presumably referring to the fact that the palms are not quite true Thrinax. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Common Name

  • Not recorded. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Uses

  • Not recorded. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

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. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Anatomy

  • Not studied. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Fossil record

  • No generic records found. (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Relationships

  • Hemithrinax is monophyletic with high support (Roncal et al. 2008) and sister to Leucothrinax with moderate support (Asmussen et al. 2006, Baker et al. in review). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Taxonomic accounts

  • Leon (1941) and Borhidi and Muñiz (1985). (Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms)A

Bibliography

    A. Dransfield, J., Uhl, N., Asmussen, C., Baker, W.J., Harley, M. & Lewis, C. 2008: Genera Palmarum. The evolution and classification of palms
    B. World Checklist of Arecaceae