Tabebuia aurea Seeds | Yellow Trumpet Tree
LATIN NAME: Tabebuia aurea
COMMON NAME: Yellow Trumpet Tree
Plant Profile
Yellow trumpet tree is a small to medium deciduous tree of the trumpet-creeper family, five to twelve metres tall, with a rounded, open crown and a trunk that is grey, fissured and often slightly crooked. In the dry season it drops its leaves entirely and then flowers, so that the whole crown becomes a mass of golden, funnel-shaped blooms with nothing green behind them. That is the display people plant it for.
The leaves, when they are present, are palmately compound with five to seven leaflets, stiff and slightly grey-green, and they return after the flowering peak. The flowers are borne in dense terminal clusters, each one about six centimetres long with a flared mouth, and they last only a few days on the tree before falling to carpet the ground.
The fruit is a long, slender capsule that ripens after the rains and splits to release papery, winged seed, which is dispersed by wind and can travel a considerable distance from the parent tree. The species is native to the savanna and dry woodland of central Brazil, Bolivia, Paraguay and northern Argentina, where it grows on sandy, well-drained soils and flowers at the height of the dry season.
It is widely planted in tropical and subtropical cities for that dry-season display, and it is one of the trees that gives the Brazilian interior its characteristic look in August and September, when the yellow crowns stand out against a brown landscape.
Science & Biotechnology
The genus has been split, and the split matters for anyone reading the medicinal literature. The species with the showiest flowers and the strongest claims to pau d’arco, the famous bark tea of South America, have been moved to Handroanthus, while Tabebuia in the narrower sense contains species such as this one. The chemistry is shared across both genera, but the commercial pau d’arco of the supplement trade comes mainly from Handroanthus impetiginosus and its relatives, not from the yellow trumpet tree.
The characteristic compounds are naphthoquinones, above all lapachol and its isomer beta-lapachone, which occur in the heartwood of many species in the family. Lapachol has shown antimalarial, antitumour and antimicrobial activity in laboratory studies, and beta-lapachone has been investigated as an anticancer agent, though clinical development has been limited by toxicity and by poor solubility. The bark tea sold as pau d’arco is not a standardised medicine, and the evidence for its use in cancer is not there.
Ecologically the species is a dry-season flowering specialist, timed to attract the large bees and hummingbirds that are active in the savanna when little else is in bloom. The flowering is brief and synchronous across a population, which saturates pollinators and then sets a heavy crop of wind-dispersed seed. The wood is hard and durable and is used locally for construction and for fence posts.
Uses & Benefits
In the garden and the street, the tree is grown for its flowering season and for its tolerance of heat, drought and poor soil. It is a good specimen for a dry lawn, a park or a wide verge, where the bare golden crown can be seen from a distance, and it is used in tropical landscaping as a seasonal marker rather than as a shade tree. It needs space, since the crown spreads, and it needs sun.
The wood is heavy, hard and resistant to decay, and it is used in its native range for construction, posts, tool handles and turnery. It is not a commercial timber in international trade, but it is valued locally, and the tree is sometimes retained on farmland for that reason.
The medicinal use of the bark follows the pau d’arco tradition, and it should be treated with caution. The inner bark is brewed as a bitter tea in South America for fever, pain, skin complaints and, more recently, for cancer, but the evidence is limited to laboratory and animal work, and the naphthoquinones involved are toxic at high doses. It is not a treatment for cancer, and anyone considering it should speak to an oncologist rather than to a supplement seller.
Ecologically, the flowers feed bees and hummingbirds and the seed feeds small birds, and the tree is a useful component of dry-forest restoration in its native range. It is not invasive where it has been planted outside the tropics, because it needs a long dry season to flower well.
Growing from Seed
Sow the papery seed fresh, on the surface of a loose, gritty, free-draining mix, and cover it only lightly, since light helps germination. Keep at twenty-two to twenty-eight degrees, in bright light, with even moisture. Germination is usually two to four weeks, and the seed loses viability within a few months, so it should not be stored for long.
Grow the seedlings on in full sun, in a free-draining mix, and pot them on as they grow. Plant out once the root has filled the container, at the start of the wet season, into a sunny, well-drained site. Water through the first two dry seasons, then only in severe drought. The tree is fast when young and can flower within four or five years from seed, and it needs little pruning beyond the removal of low branches to clear a trunk.
Our Take
This is a tree for a warm, dry garden with room to spare, and it earns its place in one week of the year, when the bare crown turns gold. The rest of the season it is a modest, useful shade tree with hard wood and no vices. Grow it for the spectacle, and do not expect the bark to do what the supplement industry claims for pau d’arco.
Related Reading
More species in the same orbit as Yellow Trumpet Tree: