Cassytha

Cassytha is a genus of some two dozen species of obligately parasitic vines in the family Lauraceae. Superficially, and in some aspects of their ecology, they closely resemble plants in the unrelated genus Cuscuta, the dodders. When fruit and flowers are absent in the field, the physical resemblance is so close that few people without technical training can tell them apart. In this respect and in their ecology the two genera present a spectacular example of convergent evolution. Nonetheless, Nickrent comments that 'Cassytha is uneqivocally assigned to Lauraceae based on (both) morphological and molecular data.' In its divergence from habits typical of the Lauraceae, Cassytha also presents examples of mosaic evolution Several species of Cassytha are regarded as pests in various regions, though as a rule they are not as serious a problem as the true dodders. Some even yield a welcome harvest of fruit, or are valued for their perceived medicinal or aphrodisiac properties, partly because, like many members of the Lauraceae, some are fragrant when bruised. Their stems make useful strings for construction of thatched roofs and certain styles of lei and the like. Probably the most useful common names for Cassytha species are laurel dodder or dodder laurel, because they look like dodder and are fragrant members of the laurel family, Lauraceae. The name love vine has merit because some species, in particular C. filiformis, are regarded as aphrodisiacs in the Caribbean region. In practice, however, the confusion between the various species of Cassytha and Cuscuta is so unavoidable that their common names are more or less interchangeable. Practically all the common names for dodder accordingly are widely applied in error to Cassytha as well, but as a matter of convenience in Florida at least, where members of both groups of plants are present as agricultural pests, a publication of the Department of Agriculture adopts the names woe vine for Cassytha and dodder for Cuscuta. Though the Lauraceae constitute a large family, with thousands of species in tens of genera, Cassytha is its only known parasitic genus, and its climbing habit also is atypical of the family; most Lauraceae are woody shrubs or trees. The genus at one time was assigned its own family, Cassythaceae, but currently agreement on its inclusion into the Lauraceae is general. As currently defined, Cassytha has a wide distribution for a genus of so few species. Most are native to Australia (including temperate regions, where they are the only native members of the family), but a few are indigenous to Africa, southern Asia, various islands, and regions in the Americas. Some species seem to have been spread inadvertently by human agency and probably by birds as well, and now occur on several continents; C. filiformis, for example, grows in Hawaii (where it is said to be indigenous), the Australasian ecozone, northern South America, Central America, southern Florida, Japan, and South Africa. It also appears to have been transported to many major islands, and now is effectively pantropical. The genus is cited as Cassytha L., Sp. Pl. 35 (1753), which means that Carl Linnaeus formally described it in 1753 in his monumental work, Species Plantarum. Otto Stapf updated the work in Flora Capensis in 1912. Cassytha is unusual among Lauraceae in at least two respects: they are scandent herbaceous plants, and they are obligate parasites. Their stems are thread-like or wiry, and like most twining species, they twine round the host clockwise as seen from the source of growth. The vines generally turn yellowish once they have established themselves on a productive host because they then reduce or stop their production of chlorophyll. Cassytha species are stem parasites, adhering to their hosts by uniseriate haustoria that generally are small and oblong. Their leaves are without stipules, alternate, simple, and easily overlooked, being minute and scale-like. Various species of Cassytha bear flowers in racemes, spikes, or heads. Depending on the species, the flowers are sessile or pedicellate. The individual flowers are hermaphroditic and bracteolate, each being attended by a bract and two smaller bracteoles. In general, the flowers are small, so much so that in many species they are inconspicuous.