Thrinax
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Thrinax is a palm genus nativeto the islands of the Caribbean and the adjacent mainland.
features
The representatives are small to medium-sized, single-stemmed unreinforced palms. They are several times blooming and hermaphroditic. The trunk is erect, columnar, smooth or fibrous and provided with ring-shaped leaf scars. There are usually numerous fibrous roots at the base of the trunk .
The chromosome number is 2n = 36.
leaves
The leaves are induplicate, fan-shaped and often irregularly divided. The leaf sheath tears open at both ends: opposite the petiole and abaxial. It dissolves into irregular fibers. The vagina is densely covered with a later falling hair. The petiole is long and slender. It is rounded to slightly furrowed on both sides, the lateral edges are rather sharp. The hastula on the adaxial side (upper side of the leaf) is conspicuous, long pointed, often curled up, the abaxial hastula is smaller, rounded or triangular and can also be absent. The leaf blade is fan-shaped, the often irregularly shaped individual segments are connected in the lower half. They are lanceolate, pointed with usually a two-part tip. The upper side of the leaf is bare, the underside often covered with scales, sometimes white. The midrib and the marginal ribs are striking.
Inflorescences
The inflorescences are between the leaves (intrafoliär). They are slender, upright to arched and twofold branched. The side axes of the first order are hanging. The peduncle is rather slender and circular in cross section. The cover sheet is short, tubular, two-keeled, hairy and opens distally. There are several bracts on the peduncle that are similar to the cover sheet, but are not keeled. They overlap each other and separate the stem. The inflorescence axis is longer than the stem and slender. There are long, tubular bracts arranged in a spiral, in whose armpits the first-order side branches sit. These have a short free section on which a double-sided, two-part cover sheet sits. The flower-bearing side branches (rachillae) arise from spiraling, narrow, triangular bracts. These are slim, rather short and stiff. On them are small triangular bracts in a spiral that carry the individual flowers. Bracteols are likely to be missing.
blossoms
The flowers are on showy stems. The perianth forms a single cup with six lobes or teeth. Usually there are 6 to 12 stamens . Their stamens are very slender, sometimes connected at the base. The anthers are elongated, the stamens attach dorsifix to the lower area of the outside of the anther. The anthers stand latrors . The gynoeceum consists of a single carpel that is unilocular and contains only one ovule . This sits basal, is upright and campylotropic , but slightly crooked, so that the micropyle points to the upper dorsal wall of the seminal compartment. Basally, the ovule is surrounded by an aril .
The pollen is ellipsoidal with slight to marked asymmetry. The germ opening is a distal sulcus , more rarely a three-way sulcus. The longest axis measures 24 to 46 microns.
Fruits and seeds
The fruit is very small and white when ripe. The remains of the stigma are at the top, and remnants of the flower cover are often also present. The exocarp of fresh fruits is smooth, the mesocarp is thin and floury, the endocarp is very thin and papery. The seed is compressed-spherical, smooth, has a smooth stigma (hilum). The ramifications of the raphe are deeply indented and cause a furrowing of the endosperm , which is otherwise homogeneous.
Distribution and locations
Two species are endemic to Jamaica . The third species is widespread in coastal locations of Honduras, Belize, Mexico, and the northern Caribbean. In Jamaica, the three species are separated according to location: Thrinax parviflora grows in dry, evergreen forests and thickets, Thrinax excelsa grows in lowland rainforests and Thrinax radiata in coastal, salt-influenced forests and thickets.
Systematics
The genus Thrinax L.f. ex Sw. is placed within the family Arecaceae in the subfamily Coryphoideae , Tribe Cryosophileae . The genus is monophyletic . It is possibly the sister group of the group from Schippia and Cryosophila .
There are three species recognized in the World Checklist of Selected Plant Families at the Royal Botanic Gardens, Kew:
- Thrinax excelsa Lodd. ex Mart. , Endemic to Jamaica
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Thrinax parviflora Sw. , Endemic to Jamaica; occurs in two subspecies:
- Thrinax parviflora subsp. parviflora
- Thrinax parviflora subsp. puberula Read
- Thrinax radiata Lodd. ex Schult. & School f. : It occurs in southern Florida and from southeastern Mexico to Nicaragua and in the northern Caribbean.
Fossil history
Fossils compared to recent species of Thrinax include leaves of Thrinax eocenica from the middle Eocene of southeastern North America ( Claiborne flora ) and of Palaeothrinax mantelli from the lower to middle Oligocene of the Isle of Wight . A pollen known as Thrinax tranquillus is very common in its form in the subfamily Coryphoideae .
supporting documents
- John Dransfield, Natalie W. Uhl, Conny B. Asmussen, William J. Baker, Madeline M. Harley, Carl E. Lewis: Genera Palmarum. The Evolution and Classification of Palms . Second edition, Royal Botanic Gardens, Kew 2008, ISBN 978-1-84246-182-2 , pp. 232-234.
Individual evidence
- ↑ a b c Rafaël Govaerts (ed.): Thrinax. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved April 15, 2020.
- ↑ a b Julissa Roncal, Scott Zona, Carl E. Lewis: Molecular Phylogenetic Studies of Caribbean Palms (Arecaceae) and Their Relationships to Biogeography and Conservation . Botanical Review, Volume 74, 2008, pp. 78-102. doi : 10.1007 / s12229-008-9005-9
Web links
- Thrinax on the homepage of the Fairchild Tropical Botanic Garden