Thrinax, Linnaeus f. ex Swartz, 1788

Henderson, Andrew, 2023, A revision of Coccothrinax, Hemithrinax, Leucothrinax, Thrinax, and Zombia (Arecaceae), Phytotaxa 614 (1), pp. 1-115 : 97-99

THRINAX

Thrinax Swartz(1788:57) was the first genus of the Thrinax unit to be described.Swartz described Thrinax parviflora from Jamaica, and subsequently numerous other species were described, often of obscure origin. It was not until the revision of Read (1975) that the genus became well understood. Read recognized four species, one of which, T. morrisii , was later recognized as a separate genus, Leucothrinax ( Lewis & Zona 2008) .

Morphology

In the following discussion, morphology is treated in detail and several attributes of Thrinax not used in delimiting species are discussed. A detailed discussion of morphology is given in Read (1975) and a detailed generic description can be found in Dransfield et al. (2008).

Stems are recorded as 1.5–18.0 m long and 5.0–24.0 cm diameter, and are always solitary. The 18.0 m length and 24.0 cm diameter records are from a specimen of T. excelsa , and this species has the largest stems and leaves ( Fig. 23A ). For T. radiata ( Fig. 23B ) and T. parviflora , stems are a mean of 3.3 m long and 10.1 cm diameter.

Leaf sheaths are split at the base ( Fig. 23C ). Leaf sheath fibers are scored as thin (usually <0.5 mm diameter), flimsy, closely woven, forming ligules at the apices. Read (1975) considered that the ligules of T. parviflora and T. excelsa were similar and Ʌ-shaped at the apex, but that the ligules of T. radiata were different and were V-shaped at the apex. This difference has not been seen in the present study, because ligules soon disintegrate into separate fibers, and are seldom present on specimens. Adaxial hastulas are well-developed, particularly in some specimens of T. parviflora . Palmans are relatively long, without prominent adaxial veins. Middle leaf segments are relatively long and narrow with a shoulder distal to the palman apex, widest at the shoulder ( T. parviflora ), or relatively long and narrow without a shoulder distal to the palman, tapering gradually towards the apex and widest at palman apex ( T. excelsa , T. radiata ). Leaf segments are without indumentum, but have large, scattered, brownish scales on the abaxial surface. Transverse veinlets are well-developed.

Inflorescences are scored as erect, at least initially, amongst or above the leaves, with 6–15 partial inflorescences. Rachis bracts are swollen, woody, and densely reddish-brown tomentose, or closely sheathing, membranous, and brown tomentose. Rachises of the partial inflorescences are flattened in cross-section and rachillae are unevenly spaced, with some in groups. Rachillae are glabrous or granulose at or near anthesis. Pedicels are relatively well-developed and range, in fruiting specimens, from 0.6–5.0 mm long. Flowers in Thrinax are borne spirally along the rachillae. The perianth is a six-toothed cupule. There are 6–9, elongate, latrorse stamens that spread irregularly at anthesis.

Fruits of Thrinax range in size from 4.4–7.1 mm long and 4.4–7.3 mm diameter. Fruits are white and the surfaces are smooth or with short projections.

Seeds have smooth surfaces. As seen in longitudinal section, they are intruded by the hilum more than half way, usually from the base to the apex ( Fig. 23D ). Embryos are subapical to lateral.

Figures

FIGURE 23. A. Thrinax excelsa. B. Thrinax radiata. C. Split leaf sheath bases. D. Seed in longitudinal section, intruded by the hilum from the base to the apex.