Liquidambar styraciflua Seeds | Sweetgum
LATIN NAME: Liquidambar styraciflua
COMMON NAME: Sweetgum, American Sweetgum, Redgum
Plant Profile
The leaf of sweetgum is the kind you press in a book: a star of five to seven pointed lobes with a straight, untoothed edge and a long stalk, and it turns a clean red, orange and purple in autumn that holds on the twig long after the tree has dropped most of its shade. Crush the leaf and it smells of balsam, the scent that gave the tree its common name and its place in the old apothecary jar.
The star shape is so fixed that the leaf is a classroom example of palmate venation, the veins running like spokes from the base of the blade to the tip of each lobe. A young tree can throw the odd three- or nine-lobed leaf among the fives, but the five-lobed form dominates, and the straight lobe edge is the quick tell against the toothed maples it is often mistaken for.
The seed sits in a woody, spherical head armed with short spikes, each head a cluster of many two-valved capsules, and when it opens the small winged seeds drift out a few at a time through the dry season. The spiky ball is the most lasting field mark of the tree, hanging on after the leaves and rattling in the wind well into winter.
The Asian Liquidambar formosana, the Formosan sweetgum, is a close relative with tail-tipped leaf lobes and a similar ball, but styraciflua keeps rounded lobe bases and a broader, more symmetrical star. The two overlap in botanic gardens around the world, and the lobe tip is the quick way to tell the American from the Asian tree.
Crushed twigs and leaves yield a small essential oil dominated by cinnamic and related balsamic notes, the same family of compounds that makes storax useful in scent work. The oil is minor next to the timber, but it explains the unmistakable smell you get when you break a green twig on a walk.
Science & Biotechnology
Sweetgum is one of the commercial sources of shikimic acid, the starting material for the antiviral drug oseltamivir, and the compound is drawn from the fermented leaf and fruit rather than from the better-known star-anise supply. That single molecule turned a common woodland tree into a strategic crop during flu outbreaks, and it remains the clearest biochemical claim to fame of the genus.
Uses & Benefits
The tree bleeds a fragrant balsam called American storax when the bark is cut, and that resin was used for centuries as a plaster and a perfume base, a use old enough that the Latin name Liquidambar means liquid amber. The balsam is the source of the ‘sweet’ in sweetgum and the reason the wood and the wound share a scent.
The wood is traded as red gum, a pale, even-textured timber used for plywood, veneer, furniture and turnery, and it works cleanly once dried. The name red gum comes from the reddish heartwood and the gummy sap, not from any relation to the eucalyptus also called red gum, so the two are easy to confuse at the lumberyard.
The hardened droplets of balsam that ooze from a wound dry to amber tears that early settlers chewed like gum, which is the plainest origin of the English name. The chew is more resin than sugar and soon loses its charm, but the habit stuck in the language long after the taste faded.
In the planting trade sweetgum sells on autumn colour that rivals any maple, and selected forms hold a near-solid red or purple that draws buyers to the nursery bench. The star leaf and the long hang of the colour are why it is planted as a street and park tree across the warm temperate world.
Growing from Seed
The seed is slow and uneven from the spiky ball, so give the cleaned seed a long cold, moist rest in sand before sowing to break dormancy and even the stand. Without the chill the ball sits through a season and comes up in dribs, which is the usual complaint of a first sowing.
Sow two seeds per module on a gritty, moist mix with the seed just covered, and keep them bright and cool until they sprout, then keep the stronger seedling. The twin sowing covers the laggards that the spiky ball tends to throw, so you are not left with an empty cell.
Young sweetgum pushes early soft growth that a late frost nips, so site the sapling where cold air drains away and guard the first flush if a frost is forecast. A year of clean top growth sets the straight stem that makes the tree worth keeping.
Our Take
Sweetgum is the star-leaf tree that pays twice, in colour and in chemistry, but mind the spiky ball underfoot and the early frost on the tip. For a second sweetgum try the Asian Formosan sweetgum (Liquidambar formosana), and for the autumn-display company plant the red maple (Acer rubrum) or the Japanese maple (Acer palmatum). Stratify the ball, dodge the frost, and let the leaf do the selling.
Related Reading
More species in the same orbit as Sweetgum: