About Enterolobium timbouva Mart.
Enterolobium timbouva Mart., commonly known as guanacaste, is a medium-sized to large tree that grows 25–35 m (82–115 ft) tall, with a trunk reaching up to 3.5 m (11 ft) in diameter. Unusually for a tree of this size, it completely lacks buttresses. Its bark is light gray with prominent dark reddish-brown vertical fissures; in young saplings, these fissures are closer together, and their overlap gives guanacaste sapling bark a characteristic reddish hue. Bark on older specimens is often broken, chipped, or scarred.
The crown of the guanacaste is broad and widely spreading. The height of the first branch along the trunk and overall tree shape vary substantially between individuals and depend on habitat. Guanacaste frequently grows as a single specimen in open sunny pastures, where massive, extended horizontal limbs grow low on the trunk, forming a giant, hemispherical, widely spreading crown. In forests, where competition for light is intense, trees grow taller, branching begins higher on the trunk, and the overall tree shape is narrower, though even canopy-level trees still maintain rounded, hemispherical crowns.
The leaves are alternate and bipinnately compound, 15–40 cm (5.91–15.75 in) long and 17 cm (6.69 in) broad, with a 2–6 cm (0.79–2.36 in) petiole that holds four to 15 pairs of pinnae. Each pinna bears 40–70 slender, oblong leaflets, 8–15 mm (0.315–0.591 in) long by 2–4 mm (0.079–0.157 in) wide. A small, raised, oval gland grows near the base of the twiggy petiole. Leaves are only found on the outer layer of the crown, but they are abundant enough to create a moderately dense, green canopy. Guanacaste is evergreen, or briefly deciduous for 1–2 months during the dry season. Most foliage is shed in December at the start of the dry season, and a growth surge begins in late February that redevelops a fresh, thick crown by April.
Inflorescences form at the same time as new leaf growth, emerging as globular clusters 3 cm (1.18 in) wide in the axils of new leaves. Each spherical white flower head sits on a 4 cm (1.57 in) long stalk, and is made up of around 50 individual flowers, with thousands of thin filamentous stamens as its most visible feature. Each individual flower has about 20 stamens and one pistil, joined at the base by a short green tubular corolla and an even shorter calyx, with a total length of just 5 mm (0.197 in). Guanacaste flowers are very fragrant, and their scent can carry many meters in all directions during peak flowering. In Manuel Antonio National Park near Quepos, Costa Rica, flowering runs from late February to early April.
After flowering ends, fruiting does not begin immediately. Instead, small green pods first appear high in the crown 9–10 months after flowering, in December. The pods reach full size by February and finally begin ripening in March, a full year after flowering occurred. Fruit ripening runs from March to April, as green pods turn brown in the crown and are gradually shed. Vigorous trees produce large seed crops almost every year. By June, guanacaste seedlings can already be found germinating in the moist soil of the early rainy season.
Guanacaste fruits are large, 7–12 cm (2.8–4.7 in) in diameter, glossy dark brown, indehiscent, spirally organized pods shaped like orbicular disks. Their shape forms from the typical long, narrow, flattened pod of Mimosoideae, wound around an axis perpendicular to the pod's plane. The pods are made of thick, soft, leathery-textured tissue, and contain eight to 20 radially arranged seeds. The seeds are 14.5–17.5 mm (0.571–0.689 in) long, 7.8–11.2 mm (0.307–0.441 in) wide, 6.2–7.2 mm (0.244–0.283 in) thick, and weigh about 1 g. Guanacaste seeds are brown with a noticeable light brown or orange ring, and are very hard, with a strength and durability similar to small stones. For germination to occur, the hard seed coat must be broken to let water reach the embryo; otherwise, seeds remain dormant indefinitely.
Two other tree species, ardillo (Cojoba arborea) and iguano (Dilodendron costaricense), have similar fine-leafed bipinnate leaves and grow to a similarly large size. They can be easily distinguished from guanacaste: ardillo has tan-colored, heavily wrinkled, rough bark that is nothing like guanacaste's distinctly gray, vertically cracked bark. Iguano has serrated leaflets, which is unusual for a bipinnate tree, while guanacaste has entire (smooth-edged) leaflets.
Ecologically, guanacaste delays fruit development by roughly 9 months so seed maturation lines up with the start of the rainy season. This adaptation is thought to give germinating seedlings as much time as possible to establish root systems before the next dry season, a reproductive strategy shared by jatobá (Hymenaea courbaril) and cenizaro (Albizia saman). Like other deciduous and semideciduous species in this region, guanacaste gains water-conservation benefits from dropping leaves during the dry season. Bees frequently visit guanacaste flowers and are likely the species' main pollinators.
Guanacaste seed pods are completely ignored by native wild fauna, and accumulate on the forest floor beneath parent trees, as no native animals native to the tree's range eat the seeds. This has led to the suggestion that guanacaste is an evolutionary anachronism: its pods were likely eaten and dispersed by Pleistocene megafauna that went extinct around 10,000 years ago, such as giant ground sloths and giant bison. Today, the only effective natural seed dispersal vector besides humans is introduced horses and cattle, which consume the pods, abrade the hard seed coat through mastication to aid germination, and transport seeds to new locations. The tough seed coat, which requires puncturing for germination, is thought to be an adaptation to prevent germination while seeds are still in pods or under the parent tree at the start of the rainy season, when they would have been accessible to foraging extinct megafauna.
An insect pest common to guanacaste trees in Costa Rica's Central Valley produces spherical green galls 1.5 cm (0.59 in) in diameter on new shoots in February and March. Similar parasitism occurs on guanacaste trees in the wet southwestern lowlands around Palmar Sur.
In cultivation and use, guanacaste is one of the most majestic and aesthetically pleasing tree species in its native range. It tolerates a wide range of rainfall, temperatures, and soil conditions, and thrives in most low-elevation tropical habitats. It is highly valued as an ornamental tree, and the shade it creates forms oases on the hot, sun-baked plains of its Pacific slope habitat. It is widely grown as a shade tree for coffee plantations and for cattle shade and forage, and it improves soil fertility through nitrogen fixation. It grows in USDA Growth Zones 10–12.
Its wood is reddish-brown, lightweight with a density of 0.34–0.6 g/cm³ (0.20–0.35 oz/cu in), and water-resistant. It is used to make doors, windows, furniture, cabinets, and for shipbuilding. The timber has high chatoyance, with an average value above 20 PZC. It is considered a relatively sustainable resource for wood furniture and design, because the tree grows quickly to large sizes, making it easier to source large natural cuts up to several meters long, which is rare for slower-growing woods like oak or cedar. The town of La Cruz de Huanacaxtle in Nayarit, Mexico, gets its name from a historic cross made of guanacaste wood that once stood there.
Green unripe guanacaste pods are harvested in Mexico, and their seeds are eaten boiled. Healthy guanacaste trees produce large seed crops nearly every year, and the attractive seeds are used to make jewelry in Costa Rica. In parts of Panama, ripe seeds are heated over fire until they pop like popcorn. The seeds have a nearly 100% germination rate, and seedlings grow rapidly, often reaching over 1 m (3 ft 3 in) tall in their first year. These aggressive reproductive traits could be useful for reforestation projects, though the species is considered invasive in some places. Large trees have strong roots that can damage nearby structures.
Guanacaste is commonly used to feed all types of livestock; its foliage, fruits, and seeds are eaten by cattle, pigs, goats, sheep, and horses. The tree, also called parota, is believed to have medicinal properties. In Mexican folk medicine, the sap is thought to help treat influenza and bronchitis, and the astringent green fruit is used to treat diarrhea. The fruit and bark contain tannins, which are used for leather curing and soap manufacturing, while the sap can be used as a natural adhesive or glue substitute, or chewed as gum.
