James L. Luteyn and Paola Pedraza-Peñalosa
The New York Botanical Garden
|
|
Ledothamnus Meissner (Ericaceae: Rhododendroideae:
Phyllodoceae) is a genus of terrestrial shrubs and subshrubs of small stature,
restricted to the open, low-shrub savannas and rocky tepuis of the Guayana
Highlands of southern Venezuela (with one collection from adjacent Brazil).
The genus is characterized by whorled, decussate, ericoid leaves, polypetalous
corollas, and a warty, septicidal, woody, capsular fruit. Based on
floral structure and orientation, it is suspected that bumblebees visit
the flowers. Based on intermediate and/or unique combinations of
morphological characters in herbarium specimens and upon field observations,
there seems to be infrageneric hybridization in Ledothamnus.
Although Stevens (1969) noted that the genus combines some characters of
the Rhododendroideae and the Ericoideae, and that it may need to be accorded
its own monotypic tribal status, he maintained it in the Phyllodoceae (Rhododendroideae)
in his family revision (1971) feeling that much more information was needed
especially about the anthers, seeds, inflorescence, and indumentum.
Seven
species are here recognized. |
The genus was first revised by Maguire, Steyermark and Luteyn (1978) in their treatment of the Ericaceae for "The Botany of the Guayana Highland" series. Most of the taxa recognized in that treatment were described therein and identification of the species depended on a knowledge of flower color and stamen number. Therefore, Luteyn and Lebrón-Luteyn (1983) provided an alternative key based more on vegetative features. With the more numerous herbarium collections currently available, along with personal field experience, pickled material, and photographs of many of the species, Luteyn (1995b) again revised the genus from which this treatment is taken.
LEDOTHAMNUS Meissner in Martius', Fl. bras. 7: 171. 1863; Maguire, Steyermark and Luteyn, Mem. New York Bot. Gard. 29: 141-152. 1978; Luteyn and Lebrón-Luteyn, Acta Bot. Venez. 14(1): 170-172. 1983; Luteyn, Fl. Neotrop. Monogr. 66: 107-122. 1995. Type species: Ledothamnus guyanensis Meissner.
Decumbent to erect, terrestrial shrubs; bark thin, smooth to furrowed; indumentum consisting of unicellular hairs, multicellular, multiseriate, short- to long-stalked, glandular to eglandular hairs, and papillae; buds eperulate. Leaves ericoid, (opposite-)whorled, decussate, petiolate; blades succulent, brittle, glabrous to glandular-setose, apparently without venation, lamina also dorsi-ventrally compressed thus producing apparent margins then the apparent margins usually contiguous so as to ± obscure the seemingly papillate lower surface and forming a channel which opens up at the base, actual margins entire, strongly revolute. Inflorescence with flowers solitary, terminal or axillary (clustered at tips of new growth); floral bract one, leaf-like; bracteoles two, basal, usually leaf-like but reduced in size. Flowers perfect, (5-)6(-9)--merous with imbricate aestivation, erect or nodding; calyx continuous with pedicel, lobes distinct to base, persistent and woody in fruit; corolla polypetalous, rotate, spreading-campanulate, or ± campanulate-urceolate, petals spreading or somewhat erect, essentially glabrous; stamens usually the same number as petals, included, filaments distinct, flat, often dilated at base, glabrous, nappendaged, attached dorsally at middle of anther, anthers oblong (± pointed at base or at apex), smooth, unappendaged, dehiscing introrsely along entire length; pollen with viscin threads; ovary superior, ovoid, 5(-7 ?)--locular, strongly verrucose, usually glabrous, placentation axile but ± apical and bifid with prominent basal lobes; ovules numerous; nectariferous disc present around base of ovary; style stout, inserted, cylindric, obconic to conic, slightly swollen at apex, glabrous; stigma truncate to depressed-capitate, ± prominently bluntly papillate. Fruit a septicidal capsule, woody, oblong to ovoid, verrucose (warty), brown; seeds few, ovoid-angular but ± trigonous, ca. 0.8 mm long, without wings or tails, orangish-brown, testa reticulate-foveolate, the cells slightly elongated, thin-walled, loose from the endosperm; embryo white; chromosome number unknown.
A neotropical genus of seven species endemic to the Guayana Highland of southern Venezuela, with one collection from adjacent Brazil.
Key to Neotropical Species Back to Top
[Notes on use of key: Since many of the indumentum features are lost with age, one must be certain to check young, current-year's growth (uppermost leaves) when using the key.]
1. Calyx 2-3 mm long; petals 4-6 mm long; Cerro Duida
............ L.
parviflorus.
1. Calyx greater than 3 mm long; petals usually greater
than 6 mm long;
ranging east of Cerro Duida.
2. Pedicels 0.5-6.5 mm long, the flowers
buried amongst the leaves
or appearing
at the level of the leaf tips.
3. Leaf
and sepal margins with sessile or very short-stalked (less than
0.1 mm long) spherical glands which may coalesce and/or be glandular
at apex; petals yellow to yellowish-green; Chimantá
Massif ... L. luteus.
3. Leaf
and sepal margins glabrous, ciliate, or bearing acicular,
eglandular hairs, apex acute to mucronate; petals white (Cerro
Sarisariñama) or scarlet (Cerro Roraima and vicinity).
4. Leaf and sepal margins glabrous or puberulent (ciliate) and also
bearing acicular hairs; pedicels setose; flowers terminal;
petals
scarlet; Cerro Roraima and vicinity ......................... L. sessiliflorus.
4. Leaf and sepal margins ciliate but without acicular hairs;
pedicels without setae; flowers axillary; petals white;
Cerro Sarisariñama .................................................... L. jauaensis.
2. Pedicels 10 mm long or more, the
flowers held conspicuously
beyond the leaves.
5. Leaves
and sepals terminating in a conspicuous dark, sessile gland
(rarely with 4-7 marginal glands near apex which may coalesce);
essentially endemic to the Chimantá Massif ................... L. atroadenus.
5. Leaves
without sessile, terminal gland(s), but instead mucronate
at apex (deciduous) and margin glandular or eglandular setose;
sepals hispid all over with glandular or eglandular setae.
6. Decumbent to erect subshrubs 0.1-0.3(-0.5) m tall; leaf
blade
imperceptibly tapering into the petiole; flowers usually solitary
or in pairs at tips of new growth; calyx not puberulent or short-
pilose; petal margins entire; filaments conspicuously longer
than
anthers; Chimantá Massif ......................................... L. decumbens.
6. Erect shrubs 0.2-1 m tall; leaf blade distinct from petiole;
flowers usually clustered (up to 7) at tips of new growth; calyx
densely puberulent or short-pilose; petal margins conspicuously
erose (very rarely entire); filaments about as long as or slightly
longer than anthers; widespread but absent from the Chimantá
Massif ........................................................................ L. guyanensis.
This is a version of a taxonomic treatment of the neotropical genus Ledothamnus by James L. Luteyn, modified from "Ericaceae--Part II. The Superior-Ovaried Genera (Monotropoideae, Pyroloideae, Rhododendroideae, and Vaccinioideae p.p.)." The full treatment including specimen citations may be see in Flora Neotropica Monograph 66: 107-122 (Luteyn, 1995b). This synthesis is published with permission of The New York Botanical Garden.