American sweetgum (Liquidambar styraciflua), also known as American storax,[3] hazel pine,[4] bilsted,[5] redgum,[3] satin-walnut,[3] star-leaved gum,[5] alligatorwood,[3] or simply sweetgum,[3][6] is a deciduous tree in the genus Liquidambar native to warm temperate areas of eastern North America and tropical montane regions of Mexico and Central America. Sweetgum is one of the main valuable forest trees in the southeastern United States, and is a popular ornamental tree in temperate climates. It is recognizable by the combination of its five-pointed star-shaped leaves (similar to maple leaves) and its hard, spiked fruits. It is currently classified in the plant family Altingiaceae, but was formerly considered a member of the Hamamelidaceae.[7]
Description
Size
Liquidambar styraciflua is a medium-sized to large tree, growing anywhere from 15–20 m (50–70 ft) in cultivation and up to 45 m (150 ft) in the wild,[13] with a trunk up 60–90 cm (2–3 ft) in diameter, on average.[14] Trees may live to 400 years.[15] The tree is a symmetrical shape and crowns into an egg shape when the branches get too heavy after its first two years of cultivation.[8]
Bark and branches
Another distinctive feature of the tree is the peculiar appearance of its small branches and twigs. The bark attaches itself to these in plates edgewise instead of laterally, and a piece of the leafless branch with the aid of a little imagination readily takes on a reptilian form; indeed, the tree is sometimes called "alligatorwood".[12] The bark is a light brown tinged with red and sometimes gray with dark streaks and has a density of 590 kg/m3 (37 lb/cu ft).[14] It is deeply fissured with scaly ridges.[12] The branches carry layers of cork.[16] The branchlets are pithy, many-angled, winged, and at first covered with rusty hairs, finally becoming red brown, gray or dark brown.[12] As an ornamental tree, the species has a drawback—the branches may have ridges or "wings" that cause more surface area, increasing weight of snow and ice accumulation on the tree. However, the wood is heavy and hard with an interlocking grain,[8] but is difficult to season.[17]
Leaves
The leaves usually have five (but sometimes three or seven) sharply pointed palmate lobes.[13] They are 8–13 cm (3–5 in) wide on average and have three distinct bundle scars.[18]
They are long and broad, with a 6–10 cm (2+1⁄4–4 in) petiole. The rich dark green, smooth, shiny, star-shaped leaves generally turn brilliant yellow, orange, red, and purple colors in the autumn.[8] This autumnal coloring has been characterized as not simply a flame, but a conflagration. Its reds and yellows compare to that of the maples (Acer), and in addition it has the dark purples and smoky browns of the ash (Fraxinus).[12] However, in the northern part of its range, and where planted in yet colder areas, the leaves are often killed by frost while still green. On the other hand, in the extreme southern or tropical parts of its range, some trees are evergreen or semi-evergreen, with negligible fall color. The leaves are 8–18 cm (3–7 in) broad with glandular serrate teeth. The base is truncate or slightly heart-shaped. They come out of the bud plicate, downy, pale green, when full grown are bright green, smooth, shining above, paler beneath.[12] They contain tannin and when bruised give a resinous fragrance.[17]
While the starry five-pointed leaves of Liquidambar resemble those of some maples (Acer), Liquidambar is easily distinguished from Acer by its glossy, leathery leaves that are positioned singly (alternate), not in pairs (opposite) on the stems. Luna and Promethea moth caterpillars feed on the leaves.[19]
Flowers
The flowers typically appear in spring and persist into autumn/fall, sometimes persisting into winter. They are typically about 25–40 mm (1–1+1⁄2 in) in diameter and are covered with rusty hairs.[14] The flowers are unisexual[19] and greenish in color. Staminate flowers in terminal racemes 5–8 cm (2–3 in) long, the pistillate in a solitary head on a slender peduncle borne in the axil of an upper leaf. Staminate flowers destitute of calyx and corolla, but are surrounded by hairy bracts. Stamens indefinite; filaments short; anthers introrse. Pistillate flowers with a two-celled, two-beaked ovary, the carpels produced into a long, recurved, persistent style. The ovaries all more or less cohere and harden in fruit. There are many ovules but few mature.[12]
Fruit
The distinctive compound fruit is hard, dry, and globose, 25–40 mm (1–1+1⁄2 in) in diameter, composed of numerous (40–60) capsules.[14] Each capsule, containing one to two small seeds, has a pair of terminal spikes (for a total of 80–120 spikes). When the fruit opens and the seeds are released, each capsule is associated with a small hole (40–60 of these) in the compound fruit.
Fallen, opened fruits are often abundant beneath the trees; these have been popularly nicknamed "burr (or bir) balls",[15] "gum balls",[20] "space bugs", "sticker balls",[21] "spike balls", or "monkey balls".[22][23]
The fruit is a multicapsular spherical head and hangs on the branches during the winter. The woody capsules are mostly filled with abortive seeds resembling sawdust.[12] The seeds are about 6 mm (1⁄4 in) thick, winged, and wind-dispersed. Goldfinches, purple finches, squirrels, and chipmunks eat the seeds of the tree.[19] The seeds stratify within 30–90 days at 1–5 °C (33–41 °F) or soaked in water for 15–20 days.[18] The long-stemmed fruit balls of Liquidambar resemble those of the American sycamore or buttonwood (Platanus occidentalis), but are spiny and remain intact after their seeds are dispersed; the softer fruits of Platanus disintegrate upon seed dispersal. The long-persisting fallen spiked fruits can be unpleasant to walk on; sweet gum is banned in some places for this reason.[15] In abundance, they can leave a lawn lumpy. The winter buds are yellow brown, 6 mm (1⁄4 in) long, acute. The inner scales enlarge with the growing shoot, becoming 13 mm (1⁄2 in) long, green tipped with red.[12]