Thrinax excelsa

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Thrinax (TREE-nahks)
excelsa (ex-SELL-sah)
Te2785379.jpg
Fairchild Tropical Botanic Garden, Florida. Cultivated. Photo by Dr. Carl E. Lewis.
Scientific Classification
Genus: Thrinax (TREE-nahks)
Species:
excelsa (ex-SELL-sah)
Synonyms
None set.
Native Continent
America
America.gif
Morphology
Habit: Solitary
Leaf type: Palmate
Culture
Survivability index
Common names
Broad thatch palm

Habitat and Distribution

Endemic to eastern Jamaica. Altitude: 450-550 m asl
Fairchild Tropical Botanic Garden, Coral Gables, Florida. Photo by Geoff Stein.

An overview of Thrinax excelsa Lodd. ex Mart.

By Jose A. Grassia

Ecology and distribution

This is a Jamaican endemic palm which is restricted in its distribution, occurring only in the region of the John Crow Mountains of the easternmost parishes (county) of Portland and St. Thomas, and on Uncommon Hill, a limestone outcrop on the lower slopes of the Blue Mountains above Fruitful Vale in Portland. Its environmental requirements are rather unusual in that it is limited to the driest, best drained, most exposed situations in the wettest part of Jamaica. The John Crow Mountains are clothed with lower montane rain forest on the lower slopes, where the rainfall may be up 7600 mm per year.

That the vegetation is very characteristic of the substrate, and that drainage is strikingly illustrated, by the situation in the John Crow Mountains. In the vicinity of Winchester Peak at the southern end of the range, the deep heavy soil on the lower slopes supports a tall forest with a dense canopy. In the relatively low illumination, epiphytes are rare and the undergrowth consists mainly of seedlings, some ferns, and a few herbaceous plants.

Higher on the steep slopes below the peak, the well-drained substrate consists of a mixture of soil, decaying matter, and loose broken rock. The forest here is lower and more open, with smaller more slender trees, but with just the occasional large emergent tree. Ferns and herbaceous plants are more common in the increased illumination and abundant moisture.

At elevations between 300 and 760 m on the slopes and ridges throughout the range, the foundation rock is frequently exposed, particularly along water courses. It is peculiar that in such a wet environment, the exposed rock is usually devoid of vegetation other than the palm Thrinax excelsa, which dominates the forest on nearly all exposed solid rock. Winchester Peak, at the southern end of the John Crows Mountain, receives less rain than nearby areas. The southeast face of this peak is dominated by a palm forest of T. excelsa at between 450 and 530 m elevation.

Throughout the rest of the range of the John Crow Mountains, the forest is considerably denser and more typical of lower montane rain forest, primarily because of the greater rainfall. On Uncommon Hill, in the northeastern foothills of the Blue Mountains and in the John Crows, where the rainfall is consistently high, T. excelsa occurs only on rocky outcrops at the higher elevations.

An occurrence of this species was recently found on a rocky hill near the mouth of the Rio Grande. (Jose A. Grassia)

Description

Large to medium palm, 3-11 m tall, caudex columnar 12.5-16.0 cm in diameter; leaf sheath 70-90 cm long, apex long linguiform, soon tearing away from petiole, not net-like, densely tan velvety throughout; petiole 1.6-2.2 m long, densely persistent white to tan velvety lepidote abaxially, 4.0-4.5 cm wide at sheath, 2.5-3.9 cm wide at apex; hastula irregularly truncate to broadly acute 1.8-2.5 cm long, 3.4-3.9 cm wide, abaxially often with a obtuse prominence to 4 mm long near the middle; unexpanded blade portion densely white to tan lepidote on all surfaces. Leaf blade when expanded 2.3-3.5 m in diameter, circular in outline but with the outer segments not overlapping, free portion of segments drooping slightly; leaf relatively flat 45-100 cm broad; segments 55-65 in number, narrowly obtrullate, 114-172 cm long, 4.4-7.4 cm wide, widest at the sinus, fused for 45-100 cm in the leaf, rather uniformly throughout the blade, slightly longer toward the upper center, bifid at apex, 3-10 cm deep, abaxial surface white to silvery densely lepidote with interlocking fimbriate hyaline scales. Inflorescences 140-170 cm long, always arching at anthesis, primary bracts brown with rufous appressed scales, primary branches 15-17 in number, about 27-30 cm long at anthesis, with 37-47 rachillae each, glabrous, pink to purple at anthesis; flowers rosy pink, fragrant, pedicelled, 90-114 per rachilla, bracteoles shorter than the pedicels; stamens 7-10 in number, anthers 1.4-1.9 mm long, exceeding pistils in length, stigmatic area a simple slit in the apex of the style. Fruit 8.0-10.1 mm in diameter, pedicels 0.4-3.5 mm long; rachillae up to 17.7 cm long, lowermost 3.7-4.5 mm thick at the point of insertion on rachis; seed 5.9-6.0 in diameter, completely intruded from base to apex by testa. Haploid chromosome number, n= 18. (Jose A. Grassia)

The genus Thrinax, in common with Hemithrinax, Coccothrinax and Zombia of the Thrinax alliance. The genus is further distinguished by the splitting leaf sheath. (Jose A. Grassia)

Culture

Cold Hardiness Zone: 10b

Comments and Curiosities

Native to rocky cliffs and ridges in the mountains of Jamaica, this species is without doubt the most beautiful Thrinax. It has stunning, leathery and large, circular fan leaves that are up to 3 m (10 ft.) across and silvery below. It adapts well to cultivation in the tropical or subtropical garden and looks best in a sheltered situation. (RPS.com)



External Links

References

Phonetic spelling of Latin names by edric.

Special thanks to Geoff Stein, (Palmbob) for his hundreds of photos.

Special thanks to Palmweb.org, Dr. John Dransfield, Dr. Bill Baker & team, for their volumes of information and photos.

Glossary of Palm Terms; Based on the glossary in Dransfield, J., N.W. Uhl, C.B. Asmussen-Lange, W.J. Baker, M.M. Harley & C.E. Lewis. 2008. Genera Palmarum - Evolution and Classification of the Palms. Royal Botanic Gardens, Kew. All images copyright of the artists and photographers (see images for credits).

Consulted bibliography

Acevedo-Rodríguez, P y Mark T. 2012. Strong Catalogue of Seed Plants of the West Indies. Smithsonian Contributions to Botany. Number 98. Smithsonian Institution Press City of Washington.

Duno de Stefano R. y C. E. Moya. Clave para las especies de palmas de la península de Yucatán mexicana

Leiva Sánchez, A. CUBA Y SUS PALMAS Instituto Cubano del Libro, Editorial Gente Nueva, Palacio del Segundo Cabo, O’Reilly Nro. 4, La Habana Vieja, Ciudad de La Habana, Cuba

Morici, C. 2000. The Genus Thrinax in Cuba. Palms Volume 44 (2)

Read, R. W. 1975. The Genus Thrinax (Palmae: Coryphoideae). Smithsonian Contributions to Botany Number 19. Smithsonian Institution Press. City of Washington



Many Special Thanks to Ed Vaile for his long hours of tireless editing and numerous contributions.

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