Thalia geniculata
Thalia
arrowroot, bent alligator-flag, fire-flag
alligator-flag
unbranched below inflorescence;
leaves all basal or rarely with single cauline leaf borne above elongate (0.7–2.5 m) internode.
homotropic;
sheath not auriculate, spongy, containing prominent air spaces;
blade plain green, ovate to elliptic.
lax, broadly spreading to pendeant, paniclelike array, up to ca. 0.6 × 1 m;
scapes 0.8–2.5 m;
rachis not pruinose;
internodes 5–20 mm;
bracts not pruinose, green or streaked or tinged with purple, narrowly ovate, 1.3–2.8 cm, herbaceous, sparsely to densely villous.
branched, branches short and upright to elongate and arching;
rachis internodes conspicuously zigzagged;
bracts deciduous, both bracts and prophylls falling with flower if fruit not set, leaving proximal portion of rachis bare, each bract subtending 1 flower pair, herbaceous to leathery;
prophylls not evidently keeled, membranous;
secondary bracts absent;
bracteoles absent.
sepals 0.5–2 mm;
outer staminode faint lavender to purple, 15–20 × 5–10 mm;
callose staminode base yellow, apex purple, apical rim, reflexed, petal-like.
self-fertilizing [outcrossing], pale to dark purple (corolla and staminodes);
sepals persistent in fruit, 0.5–3 mm, membranous;
corolla tube 1–6 mm, corolla lobes subequal to strongly unequal;
outer staminode 1, petal-like, showy;
callose staminode mainly fleshy, narrow apical rim petal-like; cucullate staminode with 2 appendages, subterminal, finger-like;
stylar movement helical when tripped;
styles with 1 appendage, elongate, straplike.
ellipsoid, 9–12 × 6–7 mm.
capsules, 1-seeded, nearly globose to ellipsoid, pericarp thin, indehiscent.
smooth dark brown to black, ellipsoid, 7–10 × 5–6 mm.
dark brown, nearly globose or ellipsoid, smooth;
perisperm canals 2, curved;
aril reduced.
= 6.
= 18 (Senegal) 2n = 26 (in cultivation).
Thalia geniculata
Thalia
This species has the widest distribution known for any of the Marantaceae, occurring in both Africa and the Americas. Because of the marked lack of variation among the African populations, it is believed that its occurrence in west Africa was a historically recent, probably accidental, introduction (L. Andersson 1981b). The variation in pubescence and bract size within the American continent has been used as the basis for describing additional species or varieties (L. Andersson 1981b). Populations of Thalia geniculata with a striking red-purple coloration on the petiole, sheath, and pulvinus were described as T. geniculata f. rheumoides Shuey (A. G. Shuey 1975) . Such homogeneous populations are to be expected in a mainly selfing species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Thalia is not closely related to any of the other Neotropical genera (L. Andersson 1981), and it is the only genus of Marantaceae that is strictly aquatic. The cucullate staminode bearing two appendages, the helical stylar movement, and the appendaged style are unique within the family. Also unique is the prevalence of various air chambers in the leaf sheath and petiole, a specialization for the aquatic habitat, which gives the sheath its distinctive spongy texture. Dispersal by water is probably the most common means of dispersal: a gas-filled space between the seed and the fruit wall in Thalia makes the fruit buoyant (C. J. Grootjen 1983). Fruits of T. geniculata have also been reported to be eaten by ducks (W. L. McAtee 1915). Carpenter bees (Xylocopa spp.) are reported to pollinate T. geniculata in Costa Rica (T. Hartgerink et. al. 1978) and in cultivation in Asia (R. Classen-Backhoff 1991).
The widely varying chromosome numbers reported for species of Thalia probably represent errors or misinterpretations. Chromosome counts in Marantaceae are difficult, and few taxa have been adequately studied.
Species 6 (2 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaves glabrous adaxially; inflorescences lax, broadly spreading to pendant, paniclelike array; rachis internodes 5–20 mm; bracts not pruinose, green or streaked or tinged with purple | T. geniculata |
1. Leaves pilose at base adaxially; inflorescences erect, tightly clustered, compact array; rachis internodes 2–3 mm; bracts markedly pruinose, appearing whitish, red-brown to red-purple beneath waxy coating | T. dealbata |
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