The Flowering Plants of Hawaii
Part 56 Dioscoreaceae-Eriocaulaceae-Heliconiaceae
The yam family, Dioscoreaceae, consists of three genera and about 630 species all but a few belonging to Dioscorea. The family is mainly tropical with a small number of species in warmer parts of Europe. Members of the genus have been cultivated for a very long time owing to the nutritional value of their tubers.
Authors of the Manual list two species that have become naturalized and one that “persists” but does not appear to have become naturalized. Two of these, D. bulbifera (see image), hoi in Hawaiian, and D. pentaphylla, pi`a, in Hawaiian (see image), were apparently let go wild. Dioscorea alata (see image), the persistent species, known as uhi in Hawaiian, was the cultivated yam. Krauss informs us, with other information, that only a few varieties were brought by the Polynesians but many cultivated varieties were selected by islanders in order to take advantage of different soil types and growing conditions. Despite its importance as a food crop in other parts of the Pacific, uhi was not as important to the Hawaiians as taro. Nonetheless, uhi provided some variety in the diet; the other two species were eaten only in times of famine and, during those times, were harvested from the forests where they were growing wild. Dioscorea bulbifera produces tubers that are bitter, hence the English name bitter yam, and were eaten only after toxic substances had been removed by treatment with lime and long soaking in running water. (This is a common practice. For example, in the case of the preparation of the tapioca (not related to yams), roots of Manihot esculenta are crushed and washed to rid them of cyanide producing substances.)
Of no relevance to the Hawaiian yams but interesting nonetheless is the fact that several species of Dioscorea are cultivated commercially for isolation of diosgenin, a steroidal sapogenin used for the synthesis of medicinally important compounds such as progesterone and cortisone. The chemical synthesis of these compounds is exceptionally difficult and costly, but yams make the fundamental molecule, diosgenin, in significant quantities. Diosgenin need only be modified to yield the compounds of interest.
A species of Eriocaulon, identified only as Eriocaulon sp. A (standard botanical notation of an unidentified species), was collected only once as a roadside weed in on the Big Island. I have not visited the site and have been unable to locate a photograph. It is called ‘pipe-wort’ based on its appearance of a spray of slender stalks emerging from its base. It grows in wet, marshy places.
Heliconiaceae consist of the single genus Heliconia with upwards to 200 species. The family has two centers of diversity, tropical America and the western Pacific. Three species of Heliconia that have become established in the islands are listed in the Manual one of which, H. bihai (image), is illustrated here. This species is native to the Caribbean and South America. Two other species, both commonly seen in gardens in the islands but apparently not naturalized, are H. rostrata (see image) and H. psittacorum (see image). These are some of the most attractive of tropical plants which, understandably, attract the attention of collectors and breeders.