Thespesia populnea Seeds | Portia Tree
LATIN NAME: Thespesia populnea
COMMON NAME: Portia Tree
Plant Profile
The portia tree is a small, fast-growing evergreen of tropical coasts, six to ten metres, with a dense, rounded crown of broad, heart-shaped, glossy leaves and a trunk that is short and often leaning.
The flowers are the reason it is planted: wide, cup-shaped, five-petalled, bright yellow when they open and turning deep maroon at the centre, then fading to pinkish-purple by the following day before they drop. They open in succession over much of the year in warm climates, so the tree is rarely without some colour. The fruit is a flattened, round capsule, two to three centimetres across, that splits into five valves to release seeds wrapped in a fibrous coat. It is a strand plant, growing just above the tide line on sandy shores across the Indian and Pacific oceans, and its seeds float and remain viable in salt water for weeks.
Science & Biotechnology
The portia tree is one of the classic examples of sea-dispersed tropical shore flora, and its natural range is impossible to disentangle from human transport, since it was carried and planted across the Pacific by voyagers long before European ships arrived. The seeds’ buoyancy and salt tolerance explain the coastal distribution; the tree’s tolerance of wind, salt spray and poor sand explains why it holds the shoreline.
The genus is placed in the mallow family and is closely related to cotton, and its seed contains gossypol-like sesquiterpenes, the same class of compound that makes cottonseed toxic, which is one reason the fruit is not eaten. The wood is fine-grained, hard and takes a high polish, and it has been used for carvings and bowls for centuries.
Uses & Benefits
The wood is the traditional treasure: dark, dense, with a fine figure, it was the material for Hawaiian milo bowls and calabashes, for canoe parts and for carved figures, and it is still worked by craftspeople. The tree is planted for shade, for wind protection and for the look of its flowers, and it is one of the best small trees for a coastal garden, where salt and wind defeat most ornamentals.
The leaves are used in the Pacific as a wrapping for food and as a poultice, and the bark and fruit have a place in local medicine, though the plant is not a standard herbal. It also makes a good hedge or screen, since it clips well and regrows quickly, and its dense crown gives useful privacy on a small coastal plot.
Growing from Seed
The seed coat is hard and should be nicked or filed, then soaked in warm water overnight before sowing. Sow in a sandy mix at twenty-five to thirty degrees, in bright light, and keep the medium moist but not wet; germination is usually within three to six weeks.
The seedlings are fast and can be planted out within a year in tropical climates, though in cooler regions they need a glasshouse. Plant in full sun, in well-drained soil, with shelter from the strongest wind while young. The tree tolerates sand, coral rubble and poor soil, and it is drought-tolerant once established, but it is not frost-hardy and will be cut down by even a light freeze.
Our Take
A beautiful coastal tree with superb timber and a real place in Pacific craft; tropical only. Warm coasts only, and worth the space where frost never comes.
Related Reading
Gardeners who grow Portia Tree often pair it with these related subjects: