Description: Amargo has a cylindrical trunk that is usually straight and columnar and that rarely exceeds 50 cm in diameter. The species sports relatively few branches and they are found clustered somewhat erratically and asymmetrically along the top fifth of the tree. These branches are long, often angular and leggy, and extremely flexible. Together with the relatively thin leaf cover, they produce a crown that is airy and open. Amargo bark is mostly smooth and gray-white in color.
The
tree's leaves (20 cm by 4 cm), clustered at branch ends,
are simple and alternately arranged. Thick and leathery, they
are narrowly elliptical in shape, with rounded or acute apices
and long petioles (2.5 cm). The blades are bright green and glossy;
bearing marked parallel (not net-like) secondary venation. Leaf
margins and primary veins are characteristically yellow. A light
gray, fine, velvety pubescence covers Amargo twigs, flower calyxes,
and leaf undersurfaces - giving these structures an unusual, whitish
cast. New leaf growth occurs in May and June and adds to the foliage
already present - the tree is never completely bare. Flowers
are produced in large, densely-packed terminal panicles that slightly
resemble heads of broccoli. Each flower (1 cm by 0.3 cm) has a
narrow tubular corolla composed of five narrow, yellow petals
(fused at their bases) that is set in a five-pointed, cup-shaped
calyx. Five minute stamens are attached to the inside of the corolla
and the short pistil remains hidden in the flowers center. Blossoms
emit a strong, sweet fragrance that is often notable from the
ground. Amargo's flowering period is an annual event of long duration,
with most trees blossoming between late June and mid September.
(In 1991, a secondary - but profuse and widespread - flowering
was observed in December). Fruits set within a couple of
months of flowering and reach full size (15 cm long by 9 cm wide)
by January. Each is a flat, disk-shaped capsule composed of two
dehiscent valves. Tan or creme colored, the capsule's exterior
is made soft and velveteen by the presence of a trichomic layer,
while its inner surface is very rough and wrinkled - probably
to keep the papery seeds from adhering to it. In mid-June - almost
exactly a year after flowering began - the pods begin to open:
splitting longitudinally and with each valve bending a full ninety
degrees away from its initial position. About twenty, tissue-thin,
disk-shaped samaras (8 cm in diameter) then begin to peal off
the inner surface of the pod, dislodged by wind gusts. Each flat
seed (3 cm) is surrounded by a translucent circular wing, giving
the whole structure an unusual but easily recognizable appearance.
(Their shape is so unusual that new visitors to Costa Rica have
been known to mistake them for some sort of preconceived exotic
tropical arthropod when encountered unexpectedly in the forest!)
Fruiting continues from June through August. (In 1992, after the
December '91 flowering, fruits were observed from July through
November). Crop size is extremely variable between seasons, and
Amargo crowns range from being packed with these heavy pods to
bearing only one or two.
