Taxonomy of Haptanthus Goldberg & C. Nelson

Haptanthus is known from only a single collection despite several attempts to recollect it. Because of its unique inflorescence and flowers, and the specimen's lack of fruit, the original authors were unable to assign it to an existing family. After 12 years Nelson described it as the type of a new family, Haptanthaceae. The original authors mainly described and illustrated the gross morphology, pistil anatomy, and pollen of Haptanthus. In attempting to assign it to a family, eight familial placements were considered and reasons were given for their rejection. In the present paper additional characters of the leaf, stem, and pistil, mainly anatomical, are described and illustrated. Most of the wood characters are archaic (primitive). Haptanthus has a suite of characters indicating that it is probably wind-pollinated. Consideration of all the characters studied to date, and examination of additional literature and herbarium specimens of several families, enable us to suggest Flacourtiaceae and Euphorbiaceae as the closest relatives of Haptanthaceae. Recently, Flacourtiaceae has been suggested by another author. Key characters of the three families are compared in a table.