Geonoma triglochin Burret (1930c: 8)

Henderson, Andrew, 2011, A revision of Geonoma (Arecaceae), Phytotaxa 17, pp. 1-271 : 150-152

64. Geonoma triglochin Burret (1930c: 8) . Type: COLOMBIA. Caquetá: Sucre, 10 July 1926, G. Woronow & S. Juzepczuk 5858 (holotype LE n.v., holotype image US!).

Plants 2.2(1.5–4.0) m tall; stems 2.3(0.2–8.0) m tall, 1.7 cm in diameter, solitary, cane-like; internodes 1.2 cm long, yellowish and smooth. Leaves 17(10–25) per stem, undivided or irregularly pinnate, not plicate, bases of blades recurved against the rachis; sheaths 18.6(10.0–27.5) cm long; petioles 9.0(0.0–35.0) cm long, drying green or yellowish; rachis 84.7(38.5–160.0) cm long, 6.7(2.7–15.7) mm in diameter; veins not raised or slightly raised and triangular in cross-section adaxially; pinnae 3(1–8) per side of rachis; basal pinna 49.5(32.0–75.0) cm long, 28.8(10.2–53.0) cm wide, forming an angle of 21(7–44)° with the rachis; apical pinna 21.4(9.0–34.8) cm long, 17.2(7.5–28.7) cm wide, forming an angle of 32(20–52)° with the rachis. Inflorescences branched 1 order; prophylls and peduncular bracts not ribbed with elongate, unbranched fibers, flattened (if tubular, narrow, and elongate then not ribbed), deciduous or persistent; prophylls 17.4(7.5–33.0) cm long, not short and asymmetrically apiculate, the surfaces not ridged, without unequally wide ridges; peduncular bracts 27.2(20.7–40.0) cm long, well-developed, inserted 2.9(0.5–7.0) cm above the prophyll; peduncles 37.5(21.0–50.0) cm long, 5.4(2.5–10.3) mm in diameter; rachillae 5(3–9), 17.6(7.5–33.5) cm long, 5.1(2.7–10.6) mm in diameter, the surfaces without spiky, fibrous projections or ridges, drying brown or yellow-brown, without short, transverse ridges, not filiform and not narrowed between the flower pits; flower pits spirally arranged, glabrous internally; proximal lips with a central notch before anthesis, often the two sides of the notch overlapping, not recurved after anthesis, not hood-shaped; proximal and distal lips drying the same color as the rachillae, not joined to form a raised cupule, the proximal lip margins overlapping the distal lip margins; distal lips well-developed; staminate and pistillate petals not emergent, not valvate throughout; staminate flowers deciduous after anthesis; stamens 6; thecae diverging at anthesis, inserted directly onto apiculate filament apices; anthers not short and curled at anthesis, usually elongate, spiraled and twisted or sometimes remaining straight; non-fertilized pistillate flowers deciduous after anthesis; staminodial tubes lobed at the apex, the lobes spreading at anthesis, acuminate, those of non-fertilized pistillate flowers not projecting and persistent after anthesis; fruits 12.9(10.0–16.0) mm long, 10.4(7.6–12.7) mm in diameter, the bases without a prominent stipe, the surfaces not splitting at maturity, without fibers emerging, not bumpy, not apiculate; locular epidermis with operculum, smooth, with pores.

Distribution and habitat:— From 0°00’– 12°35’S and 71°18’– 78°38’W in the western Amazon region in Colombia, Ecuador, and Peru at 735(200–1500) m elevation in lowland or montane rainforest ( Fig. 41 ).

Taxonomic notes:— Geonoma triglochin is a member of the G. macrostachys clade, within which it is closely related to G. oldemanii and G. umbraculiformis . It differs from the first in its prophylls and peduncular bracts which are not ribbed with elongate, unbranched fibers; and from the second in its fruit surfaces which do not split at maturity.

Subspecific variation:— No traits except for leaf division vary within this species. There is geographic discontinuity, and specimens come from three areas, one in Ecuador and adjacent Colombia and Peru, and two in southern Peru. However, there are too few specimens to test for differences. There is an isolated, low elevation population in Amazonian Ecuador that differs significantly from other populations in nine variables. However, it is not known if the gap between this population and other, sub-Andean ones is an artifact of insufficient collecting.

There is geographical variation in this species. Regression shows there are significant associations between elevation and nine leaf and four inflorescence variables. Squared multiple R for the regression of sheath length on elevation is 0.75, rachis length 0.63, rachis width 0.36, basal pinna length 0.70, basal pinna width 0.82, basal pinna angle 0.22, apical pinna length 0.57, apical pinna width 0.33, apical pinna angle 0.51, peduncle width 0.18, rachilla length 0.48, fruit length 0.43, and fruit diameter 0.56. In particular, with increasing elevation there is a change in leaf shape, with pinnae becoming shorter and narrower with wider angles. For inflorescences, peduncles become narrower, rachillae shorter, and fruits smaller with increasing elevation.

Figures

FIGURE 41. Distribution maps of Geonoma triandra, G. triglochin, G. trigona, and G. umbraculiformis.