Quararibea asterolepis Pittier
Bombacaceae MOLENILLO
Tree: Common evergreen canopy tree (25-35 m) found growing in low-lying primary forests with wet, poorly drained soils where it can sometimes form relatively pure, single-species stands. An ecologically important species,Molenillo produces copious quantities of highly sought after fruits on a bi-annual basis. Its unusual bark and thin, table-like buttresses make it a visually intriguing specimen as well.
Description: Though irregular, Molenillo possesses one of the most striking trunks (80 cm) to be found among tropical forest trees. Its bole is generally angular and bending as it rises up through the understory, and it is creased by deep folds and ridges along much of its length. Projecting outward from the base are exceptionally thin, flat, and straight buttresses that meld with the trunk at a height of about one and a half meters. Meanwhile the whole tree is textured by very smooth bark, mottled with dusky shades of brown and green. Exfoliation occurs as the thin, irregularly shaped, tan-brown strips peal away, revealing the fresh green color of the underlying cortex. The overall effect is often breathtaking – some of the most graceful and picturesque trees to be seen in the jungle are Molenillos. Along the upper third of the trunk, relatively short, horizontal branches emerge, producing a moderately thick and narrow crown. Leaves are simple, alternate, and relatively large, varying in size from 14-22 cm in length by 7-8 cm in width. They are elliptical in shape, with rounded or sometimes pointed (mucronate) apices and 1 cm petioles. Blade surfaces have a rough, sandpapery texture. In the trees, leaves are neatly arranged in a single plane, alternating on either side of the branch that supports them (2-ranked). Often, they sag, drooping away from the twig and clearly exposing its upper surface – along which the tree’s fruits and flowers will appear. Starting in October and lasting through December, Molenillos cast off old, now yellowed foliage and then replace it – remaining bare for only about a week. New leaves are pale green, limp, and glossy – adding a contrasting tint and texture to the dull and dark tones dominant in the forest.
Molenillo flowers (3 cm by 2 cm) are produced singly or in small axillar clusters of up to five blossoms each. They appear close to the branch, within the doubly ranked rows of leaves, forming a marked white stripe amid the green foliage. In each flower, a green, cup-shaped calyx holds five long, narrow, fleshy, and creme-colored petals. In the center, a hollow, stalked staminate ball surrounds a slightly longer pistil that rises within it. Blossoms smell strongly and sweetly of honeysuckle and during intense flowering periods they fill the forest air with their agreeable odor. The main flowering season begins in late May, peaks in June, and lasts through July. It is moderately well synchronized, with trees in a single stand flowering in unison but with stands separated by several kilometers staggered by as many as two or three weeks in their fertility cycles. Sporadic incidents of flowering have also been observed in October, December, January, and March.
Fruits begin growth immediately, emerging from the widening calyxes and reaching a diameter of 3 cm. Green and globular but with pointed tips, they contain a moist, yellow, fibrous material surrounding two nearly hemispherical white seeds (1 cm). Particularly large fruit crops occur in two-year cycles, with intervening years witnessing smaller harvests. Activity can be very intense, causing many fruits to fall and accumulate on the forest floor until it is nearly covered. Eventually they rot, becoming infested with white fungus and maggots, and filling the heavy, humid jungle air with an acrid, musty smell. Fruiting occurs from mid-July through October, with individual stands participating during only a part of this extended period. Seeds germinate within a month of reaching the damp forest floor.
Similar Species: Though the wide, ovoid foliage with its two-tiered arrangement along the branches is highly characteristic and identifying for this species, the peculiar and readily recognizable trunk and buttress roots are perhaps the best way to distinguish Molenillo trees.
Natural History: Bees, other insects, bats (Croat, 1978) and probably hummingbirds (Stiles & Skutch, 1989) pollinate Molenillo flowers. Though blossoms appear at a time when the trees are fully foliated, their position close to the branch and between leaf tiers ensures their visibility. Fruits are eaten by a large variety of mammals and birds, among them: white-faced and squirrel monkeys, bats, Fiery-billed Aracaris, Slaty-tailed Trogons, and parrots.
The prolific fruit production seen only in alternate years may correspond to a strategy of “overproduction” in which the species produces far too many fruits for the standing parasitic fungal and insect communities to consume, thereby overwhelming them and ensuring that many seeds will survive and germinate. Later, the lack of a significant harvest for a two year interval reduces the likelihood that the predators can grow to depend upon this bumper crop of seeds and fruits – increasing their populations accordingly and to the point where they could destroy an entire harvest.
Interestingly, large mounds of partially eaten fruits and seeds accumulate in certain, apparently random, locations on the forest floor where stands of Molenillo trees reside. Possibly, they represent points directly beneath roosting sights, to which individual bats habitually return in the evenings to consume newly acquired fruits.
Molenillo leaves smell strongly and pleasantly of maple syrup after they are pressed and dried – the procedure employed in the preparation of herbarium samples. This agreeable aroma persists for years and is common to all species of the Quararibea genus. When opening an herbarium cabinet containing Quararibea samples, this intoxicating sweet maple smell is the first thing that is noticed.
Uses: Molenillo’s common name derives from the use of small trees as whipping or beating devices in the preparation of liquid refreshments. In very small saplings (2 or 3 meters), branches leave the trunk at right angles and at regular, periodic intervals: with 5 or 6 of them appearing at discreet junctions spaced out along the bole. Cut correctly, the small stem of such a sapling can be spun between the hands, causing the spoke-like branches to whip or beat any liquid they are immersed in.
The extraordinarily thin and flat buttresses have often been sawed off of standing forest trees for use as shelves or tables. Many living individuals still bear the scars where such planks were cut from them.
Distribution: Molenillos are widely distributed throughout the very humid primary forest, but are particularly common along creeksides or in depressions where the soil is poorly drained. The species has been observed in Manuel Antonio, Corcovado, Punta Leona, and Carara, being native to all of southwestern Costa Rica. It ranges from Costa Rica to Panama.
Photos: Tree Trunk Trunk2 Trunk3 Leaf Flower Flower2 Fruit Fruit2
Trees of Costa Rica's Pacific Slope 
