Sapium glandulosum (L.)
Morong
Common Name: YOS, YOS LECHOSO
Common evergreen or briefly deciduous canopy tree (15-20 m).
Notable for its thin crown and prominently fissured bole, this
species of Yos is adapted to the secondary forest, where light
levels are high and soils are droughty. Yos plays an important
role in the reclamation of storm-ravaged land by the forest and
it is a source of plentiful ariled seeds for the local avifauna.
Description: Yos trunks are commonly
cylindrical though not usually very straight. The bark is boldly
patterned by dark, deep fissures that meander vertically up the
bole and that cut its lighter gray surface into narrow strips.
Often, the trunk is further textured by prominent branch scars
manifest as raised and horizontally-stretched knobs that are periodically
spaced along its length. If the bark, twigs or leaves of this
species are cut or broken, a thick, white, latex-containing sap
is exuded. Branches and twigs are fat and relatively few in number.
This, combined with a spare covering of foliage, produces a very
open and airy crown. The leaves (15 cm by 3.5 cm) are simple,
alternate, finely serrate, and long petioled (2 cm). They appear
to encircle the twigs and branches that bear them (and are thus
said to be arranged in whorls - a relatively unusual pattern that
serves as a reliable identifying characteristic). Blade shape
is elliptical and their short, stubby drip-tips are thickened
and partially folded. Two pointed glands protrude from the petiole
near the base of the blade. Foliage is completely shed in March,
and then renewed almost immediately as the tree enters the growth
portion of its annual cycle. Yos flowers are borne on reddish-green
terminal spikes (15 cm), with each inflorescence containing the
separate flowers of both sexes. Male blossoms, more numerous and
smaller, are composed of discreet clumps of red stamens and they
are arranged along the distal three quarters of the spike. Female
blossoms - green globular (4 mm) structures topped by three-part,
divided pistils - occupy the spike's proximal end. Flowers appear
in late March and last until early June. The fruits are
capsules (1.5 cm) that develop from the ovaries of the female
flowers. Numbering three or four per spike, each capsule dries
and opens into three sections. An equal number of red-ariled seeds,
suspended at the ends of a small stalks found inside the capsule,
are then revealed. The bright red arils - in full view of wildlife
- are spongy and contain a sweet-smelling, milky liquid. Fruiting
occurs from late July to early September. Seeds germinate soon
(within a week or two) after coming into contact with the moist
forest floor.
Natural History: Yos flowers
are pollinated by bees and other flying insects. 
After this has occurred, the
male end of the flower spike dies and drops off, leaving only
the female flowers to develop into fruiting capsules. Once mature
and open, the ariled seeds become an obvious and easily detectable
food source for animals - especially birds. Pale-vented Pigeons
have been observed harvesting these seeds in large flocks. Presumably,
the seed is regurgitated or expelled in droppings after consumption
and thus dispersed a good distance away from the parent tree.
Apparently, white-faced monkeys harvest Sapium fruit as well (Croat,
1978).
Yos trees and saplings are sturdy and resistant to drought and
excessive sunlight and are thus good pioneer plants. They frequently
are among the first to invade clearings caused by tree-falls,
landslides, or human intervention. They are also good competitors
on steep slopes where soils are thin and xeric conditions are
prevalent. Saplings one meter tall have been observed in storm-damaged
sites after only two years of regeneration.
Another member of the Sapium genus, S. sebiferum, is the
Chinese tallow tree and the greasy material surrounding its seeds
is used in making soap and candles. (Radcliffe-Smith, 1978).
Interestingly, Sapium-type flower spikes, containing spatially
separate male and female flowers, are also common in the Euphorb
genus Croton (see C. schniedeanus).
Uses: Yos has potential for use
in reforestation programs, where poor, droughty soils in sunny
locations are to be reclaimed. Well adapted to such harsh conditions,
this secondary species is capable of improving and stabilizing
the environment so that other, more sensitive but longer lived
forest trees can gain a foothold. Allen (1956) says that the wood
is pale-yellow, light, and not used.
Distribution: In Costa Rica,
this species of Sapium can be found along trail sides in
parks and amid secondary growth. Often, it can be seen growing
on dry slopes and hillsides. It ranges from Mexico to northern
South America and the Antilles.
Flower Flower/Leaf Leaf Fruit Seed Trunk
Description: Yos trunks are commonly
cylindrical though not usually very straight. The bark is boldly
patterned by dark, deep fissures that meander vertically up the
bole and that cut its lighter gray surface into narrow strips.
Often, the trunk is further textured by prominent branch scars
manifest as raised and horizontally-stretched knobs that are periodically
spaced along its length. If the bark, twigs or leaves of this
species are cut or broken, a thick, white, latex-containing sap
is exuded. Branches and twigs are fat and relatively few in number.
This, combined with a spare covering of foliage, produces a very
open and airy crown. The leaves (15 cm by 3.5 cm) are simple,
alternate, finely serrate, and long petioled (2 cm). They appear
to encircle the twigs and branches that bear them (and are thus
said to be arranged in whorls - a relatively unusual pattern that
serves as a reliable identifying characteristic). Blade shape
is elliptical and their short, stubby drip-tips are thickened
and partially folded. Two pointed glands protrude from the petiole
near the base of the blade. Foliage is completely shed in March,
and then renewed almost immediately as the tree enters the growth
portion of its annual cycle. Yos flowers are borne on reddish-green
terminal spikes (15 cm), with each inflorescence containing the
separate flowers of both sexes. Male blossoms, more numerous and
smaller, are composed of discreet clumps of red stamens and they
are arranged along the distal three quarters of the spike. Female
blossoms - green globular (4 mm) structures topped by three-part,
divided pistils - occupy the spike's proximal end. Flowers appear
in late March and last until early June. The fruits are
capsules (1.5 cm) that develop from the ovaries of the female
flowers. Numbering three or four per spike, each capsule dries
and opens into three sections. An equal number of red-ariled seeds,
suspended at the ends of a small stalks found inside the capsule,
are then revealed. The bright red arils - in full view of wildlife
- are spongy and contain a sweet-smelling, milky liquid. Fruiting
occurs from late July to early September. Seeds germinate soon
(within a week or two) after coming into contact with the moist
forest floor.
