Sesuvium is a genus of about 14 species of succulent flowering plants in the family Aizoaceae (the ice plant family), order Caryophyllales. Collectively known as sea-purslanes, its members are native to the tropics and subtropics around the world, with occurrences spanning coastal Africa, Asia, Australia, the Americas, and remote island groups such as the Galápagos and Aldabra. The genus was established by Carl Linnaeus in 1759 in Systema Naturae (Ed. 10).
Plants in Sesuvium are annual or perennial herbs, sometimes low shrubs, and are notably succulent and often papillate. Stems are prostrate to erect, frequently forming dense mats and rooting at nodes. Leaves are cauline, opposite, and equal within each pair; petioles are clasping at the base with scarious margins; blades are flat and range from linear to spatulate or ovate with entire margins. Raphides (needle-like calcium oxalate crystals) have been recorded in the leaves and stalks of at least three species. Flowers are borne singly or in small cymes from the leaf axils; each flower has five calyx lobes that are reddish on the inner surface and typically hooded near the tip; true petals and petaloid staminodia are absent; stamens number 1–30 and are frequently connate at the base. The ovary is half-inferior, 2–5-locular, with axile placentation and up to 60 ovules. Fruits are circumscissile capsules; seeds are black to brown, arillate, reniform, and shiny or dull.
The most widely distributed and studied member of the genus is Sesuvium portulacastrum (shoreline sea-purslane), a sprawling perennial found across tropical and subtropical coastlines in coastal salt marshes, mangrove margins, tidal flats, and sandy or limestone shores. Other notable members include S. maritimum (slender sea-purslane) of eastern North America and S. crithmoides (tropical sea-purslane) of west Africa. Genus synonyms include Cypselea Turpin, Halimus Rumph. ex Kuntze, Psammanthe Hance, Pyxipoma Fenzl, and Radiana Raf.
Distribution
Sesuvium is distributed throughout the tropics and subtropics worldwide, with species recorded from coastal Africa (including Angola, Benin, Botswana, and Aldabra), South and Southeast Asia (Bangladesh, Andaman Islands), Australia, the Americas (from Arizona and the Bahamas south through Brazil and Argentina), and oceanic islands including Bermuda and the Galápagos. Most species favour coastal and saline habitats.
Ecology
Species of Sesuvium are characteristic plants of saline and coastal habitats, including tidal flats, salt marshes, mangrove margins, coastal limestone outcrops, and sandy shores. The flagship species S. portulacastrum is adapted to sandy clay, sandstone, and tidal mud throughout the tropics. The plants are succulent halophytes capable of tolerating high soil salinity. Flowers of at least some species close at night or in cloudy conditions and are pollinated by bees and moths.
Cultural Uses
Sesuvium portulacastrum is consumed as a vegetable in the Philippines, where it is known as dampalit (Tagalog); it is commonly pickled and served as atchara (sweet traditional pickles). Plant extracts of this species have demonstrated antibacterial, anticandidal, and moderate antifungal activity in laboratory studies.
Taxonomy Notes
The genus Sesuvium was described by Linnaeus in 1759 (Syst. Nat. Ed. 10: 1058). Several genera are now treated as synonyms: Cypselea Turpin, Halimus Rumph. ex Kuntze, Psammanthe Hance, Pyxipoma Fenzl, and Radiana Raf. The GBIF backbone recognises Sesuvium L. within family Aizoaceae, order Caryophyllales, class Magnoliopsida. The type species S. portulacastrum was originally described by Linnaeus as Portulaca portulacastrum in 1753 before being transferred to Sesuvium in 1759; an 1891 attempt by Otto Kuntze to move it to Halimus was not accepted.
