Dioscoreaceae is a small but disproportionately interesting plant family. It gives the world its staple yams, its strangest caudiciform succulents, and some of the most theatrical flowers in the whole plant kingdom — the black “bat flowers” of the genus Tacca. This page is a hub for the family as a whole: it sets out how Dioscoreaceae is defined and organised, then indexes its four constituent genera, each of which is covered in more depth on its own page.
Taxonomy and circumscription
Dioscoreaceae belongs to the monocot order Dioscoreales, which in its current, molecularly supported circumscription (APG IV) contains only three families: Dioscoreaceae itself, the mostly myco-heterotrophic Burmanniaceae, and the small, lily-like Nartheciaceae.
Within Dioscoreaceae, the modern, broad definition is considerably younger than the family name itself. Well into the late twentieth century, botanists recognised several genera now placed here as members of entirely separate families: Tacca stood in its own family, Taccaceae; Trichopus in Trichopodaceae; and Stenomeris in Stenomeridaceae. A combined morphological and molecular study published by Caddick, Wilkin, Rudall, Hedderson and Chase in 2002 demonstrated that these genera are nested within Dioscoreaceae rather than standing apart from it, and the broader circumscription used ever since unites all four genera under a single family.
As currently accepted, Dioscoreaceae comprises approximately 650 species across four genera: Dioscorea (roughly 630 species), Tacca (around 17–19 species), Trichopus (2 species) and Stenomeris (2 species). Dioscorea alone therefore accounts for about 95% of the family’s diversity, which explains why it receives its own dedicated hub page on this site while the other three genera are introduced here.
Morphology and biology
Despite their very different public reputations — food crop, succulent curiosity, exotic houseplant — the four genera of Dioscoreaceae share a recognisable underlying plan. All are perennial herbs or vines that die back, wholly or partly, to a persistent underground or partly exposed storage organ (a rhizome, tuber or, in the succulent species of Dioscorea, a true caudex) between growing seasons. Leaves are typically broad and heart-shaped, and in Dioscorea and Stenomeris show the strongly net-like (reticulate) venation that is unusual among monocotyledons and once caused these plants to be mistaken for dicots.
Where the genera diverge most visibly is in their flowers and fruit. Dioscorea is dioecious, bearing small, inconspicuous greenish or yellowish flowers in spikes on separate male and female plants, with a winged capsule as fruit. Tacca, by contrast, produces some of the most elaborate inflorescences in the plant kingdom: umbels of small flowers subtended by broad, often blackish-purple bracts and long, thread-like bracteoles, an architecture that in several species mimics rotting flesh to attract carrion and dung flies, even where — as recent work on Tacca chantrieri has shown — the flowers turn out to be self-pollinating. Trichopus and Stenomeris, the two smallest and least-known genera, are unspecialised rhizomatous herbs and climbers respectively, with comparatively simple flowers that have kept them out of general cultivation.
Distribution and ecology
The family is pantropical. Dioscorea alone spans three major centres of diversity — tropical Africa, tropical Asia and the Neotropics — and extends into several warm-temperate regions. Tacca is centred on tropical and subtropical Asia and the western Pacific, with outlying species in Africa, Madagascar, Australia and South America. Trichopus is far more restricted: one species, Trichopus zeylanicus, occurs in the lowland forests of southern India and Sri Lanka, while the other, Trichopus sempervirens, is endemic to Madagascar. Stenomeris is confined to western and central Malesia — Borneo, the Malay Peninsula, Sumatra and the Philippines — where its two species climb in wet tropical forest.
Genus index
Dioscorea
By far the largest and most economically and horticulturally significant genus in the family, Dioscorea covers both the true yams that feed a large part of the tropical world and the caudiciform “elephant’s-foot” succulents prized by collectors. Because of its size and internal diversity, the genus has its own dedicated hub page on this site, indexing species from southern African and Mexican caudiciforms through economically important yams to ornamental foliage and temperate species.
Tacca
Tacca, the bat-flower and arrowroot genus, comprises roughly 17 to 19 species of rhizomatous herbs native mainly to tropical Asia and the western Pacific, with a scatter of species in Africa, Madagascar, Australia and South America. Its two horticultural claims to fame sit at opposite ends of the useful-to-ornamental spectrum:
- Tacca chantrieri — the black bat flower, grown worldwide as a shade-loving curiosity for its purple-black, bat-winged inflorescence with whisker-like bracteoles up to 60 cm long; native from Assam through southern China and continental Southeast Asia.
- Tacca integrifolia — the white or purple batflower, similar in structure to Tacca chantrieri but with paler, more erect bracts; native to continental and insular Southeast Asia.
- Tacca leontopetaloides — Polynesian arrowroot, an economically important species whose tubers, after careful processing to remove bitter and toxic compounds, yield a starch that was a traditional staple across the Indo-Pacific; spread as a canoe plant by Austronesian voyagers and now naturalised throughout the tropics.
Trichopus
A genus of only two species, both grown far more for scientific and ethnobotanical interest than for horticulture.
- Trichopus zeylanicus — a small rhizomatous forest herb of southern India and Sri Lanka, known locally as Arogyapacha (“the green that gives strength”). It became internationally known through the Kani tribe’s traditional use of its fruit as an energy tonic, which led to one of the first formal benefit-sharing agreements between an indigenous community and pharmaceutical researchers in India.
- Trichopus sempervirens — a far less studied species, endemic to Madagascar.
Stenomeris
The most obscure genus in the family, comprising two climbing, rhizomatous species restricted to the forests of western Malesia and effectively unknown in cultivation.
- Stenomeris borneensis — native to Borneo, the Malay Peninsula, Sumatra and Mindanao in the Philippines.
- Stenomeris dioscoreifolia — restricted to the Philippines, and, as its epithet suggests, notable mainly for its close resemblance to Dioscorea in leaf form despite belonging to a separate genus.
Cultivation notes
Cultivation needs diverge sharply across the family and are covered in detail on each genus’s own page. In broad terms, the caudiciform species of Dioscorea demand a strictly mineral, fast-draining substrate and a completely dry dormancy, while the food-crop and ornamental-foliage species of the same genus, along with the whole of Tacca, prefer sustained warmth, humidity and consistent moisture through an active growing season with only a light winter rest. Trichopus and Stenomeris remain essentially outside general cultivation and are known almost entirely from wild populations and botanical research collections.
Conservation
Conservation pressures within the family are as varied as its uses. Several economically important Dioscorea species have been overharvested from the wild for their steroidal sapogenins, used industrially in the synthesis of hormonal drugs, while narrow-range caudiciform endemics face habitat-specific threats independent of collection pressure. Trichopus zeylanicus is classed as endangered in parts of its range, its populations limited by the same forest habitat loss affecting many other endemics of India’s Western Ghats. Data on Stenomeris and on most Tacca species remain too sparse for a confident assessment, which is itself a reminder of how unevenly studied this family is beyond its most visible genus.
Reference sites
Plants of the World Online (Kew) — https://powo.science.kew.org — the nomenclatural authority used for the accepted genera and species figures cited throughout this page, including the current species counts for Tacca, Trichopus and Stenomeris.
Royal Botanic Gardens, Kew, World Checklist of Dioscoreales — https://wcsp.science.kew.org — source for the family-level species total and the genus-by-genus breakdown (Dioscorea, Tacca, Stenomeris, Trichopus) following Govaerts, Wilkin & Saunders (2007).
Bibliography
Caddick, L.R., Wilkin, P., Rudall, P.J., Hedderson, T.A.J. & Chase, M.W. (2002). “Yams reclassified: a recircumscription of Dioscoreaceae and Dioscoreales.” Taxon 51(1): 103–114. [The molecular and morphological study that merged Taccaceae, Trichopodaceae and Stenomeridaceae into a broadly defined Dioscoreaceae, forming the basis of the family circumscription used on this page.]
Govaerts, R., Wilkin, P. & Saunders, R.M.K. (2007). World Checklist of Dioscoreales: Yams and Their Allies. Royal Botanic Gardens, Kew. [Primary source for the family’s total species count and its distribution across the four accepted genera.]
Merckx, V., Bidartondo, M.I. & Hynson, N.A. (2009). “Myco-heterotrophy: when fungi host plants.” Annals of Botany 104(7): 1255–1261. [Background reference on the myco-heterotrophic families within Dioscoreales sensu APG, used to contextualise the family’s placement relative to Burmanniaceae and Nartheciaceae.]