Leucothrinax, Lewis & Zona, 2008

Henderson, Andrew, 2023, A revision of Coccothrinax, Hemithrinax, Leucothrinax, Thrinax, and Zombia (Arecaceae), Phytotaxa 614 (1), pp. 1-115 : 94

LEUCOTHRINAX

Read (1975) recognized Thrinax morrisii as a distinct species, albeit somewhat different from other Thrinax in its short pedicels and distinctive abaxial leaf surface. It was not until the use of molecular data that five distinct clades were resolved in the Thrinax unit. These clades were recognized as five genera, with Leucothrinax described as a new genus to accommodate T. morrisii ( Lewis & Zona 2008) .

Morphology

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

Stems are recorded as 0.5–6.0 m long and 5.0–14.0 cm diameter.Although the maximum stem height is 6.0 m, this appears an unusual record. Mean stem height is only 2.0 m, and in some populations stems are less than 1.0 m long. Stems are always solitary.

Leaf sheaths are split at the base. Leaf sheath fibers are scored as thin (usually <0.5 mm diameter), flimsy, closely woven, forming ligules at the apices. Palmans are relatively long, without prominent adaxial veins. However, there is a great range in palman length, from 7.2–49.5 cm, reflecting the great variability in leaf size. Middle leaf segments are relatively long and narrow without a shoulder distal to the palman, tapering gradually towards the apex, and are widest at palman apex. Segments have attenuate apices. Abaxially leaf segments are without indumentum but there are close rows of small, whitish dots between the veins on the abaxial surface, together with fewer, larger, scattered brownish or greenish scales. Tomlinson et al. 2011 consider that these small, whitish dots were composed of wax. Transverse veinlets are present and usually quite prominent.

Inflorescences are scored as erect, at least initially, amongst or above the leaves, with 8–18 partial inflorescences. This number of partial inflorescences is higher than seen in most other members of the Thrinax unit, and inflorescences are considerably longer. Inflorescences are usually branched to two orders, rarely some specimens have inflorescences branched to three orders (e.g. Correll 45292). Rachis bracts are tubular, closely sheathing, membranous, and brown tomentose. Rachises of partial inflorescences are flattened in cross-section and rachillae are unevenly spaced, some in groups. Rachillae are glabrous at or near anthesis. Pedicels are relatively short and are subtended by obscure bracteoles, but the pedicels are so short that the bracteoles appear to directly subtend the flowers. Flowers in Leucothrinax are spirally arranged along the rachillae. Perianths are shallow, six-lobed cupules. There are six, elongate stamens that spread irregularly at anthesis. The filaments are connate below and the anthers are latrorse and are often coiled and twisted.

Fruits of Leucothrinax are amongst the smallest in the Thrinax unit, and fruit length is recorded as 3.7–5.7 mm and diameter as 3.5–5.8 mm. 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 from base to about half way, as in Hemithrinax . Rarely the intrusion is from the base to the apex. Seed surfaces are smooth and embryos are subapical to lateral.