A revision of the Lennoaceae

The Lennoaceae are a small family of New World holorhizoparasites distantly related to the Boraginaceae and Verbenaceae. The three genera and total of seven species that have traditionally been accepted for the family are here reduced to two genera and four species. Lennoa is a genus of annual plants with 8-merous flowers, biseriate nodding stamens with basally spreading thecae, 7-12 vascular bundles per stem, pollen exine with a granular infrastructural layer, and diploid with n = 9. Lennoa is monotypic, with two formae of L. madreporoides recognized. Pholisma is a genus of perennial plants with 4-10-merous flowers, uniseriate erect stamens with parallel thecae, 15-25 vascular bundles per stem, tectate-columellate exine infrastructure, and tetraploid with n = 18. Pholisma (including Ammobroma) contains three very well-marked species: P. arenarium, P. culiacanum, and P. sonorae. The earliest direct mention in the literature of a plant belonging to the small parasitic angiosperm family Lennoaceae is a short description of "tlalxilotl" in the work of the sixteenth century physician-explorer Hernandez (1790). This plant, observed in the mountains near what is now Morelia, Mexico, was described as an edible, sweet-tasting herb similar to Orobanche, with a musky odor. The connection between Lennoa and the "tlalxilotl" of Hernandez was not recognized until nearly one hundred years later by Solms-Laubach (1870), in the first comprehensive study of the Lennoaceae. The conspectus of species outlined in his work forms the basis for all later taxonomic research on the family. Rydberg (1914) treated Lennoaceae in the "North American Flora" series and did not deviate significantly from Solms-Laubach's species concepts. The genus Lennoa Llave & Lexarza has since been studied by Suessenguth (1927) and Steyermark (1968), who each revised the infraspecific taxonomy of the species. Ammobroma Torrey ex A. Gray and Pholisma Nutt. ex Hooker have not since been subject to revision, except for the work of Templeton (1938, 1962) on the latter genus. Few studies on other aspects of the family have been published, although the Lennoaceae have received mention in numerous floras and phylogenetic classifications. Copeland (1935) studied the structure of the flower and inflorescence of Pholisma, while Drugg (1962) completed an analysis of pollen morphology in the family. The contributions of Kuijt to our understanding of the Lennoaceae are the first research to clearly relate structure and function in describing the parasitic habit of Pholisma (Kuijt 1966, 1967), and serve as the most comprehensive review of our knowledge of the family as part of a general work on the biology of parasitic angiosperms (Kuijt 1969). Previous studies of the family have suffered from a paucity of well-preserved, representative samples of the taxa and a lack of general descriptive data. The inability of investigators to cultivate the species (e.g., Cothrun 1969) has forced botanists to rely on herbarium specimens, which are often relatively poorly preserved. In addition, the ephemeral nature of the above-ground portions of the plants, and the predominance of highly localized populations, has resulted in an underrepresentation of Lennoaceae in herbaria. Our ongoing research into the biology and systematics of the Lennoaceae dates back to 1980. Data on the taxonomy of the family (Yatskievych 1982a) have since been reanalyzed and supplemented with additional observations. Previous papers resulting from this research have dealt with a conspectus of the taxa (Yatskievych 1982b), pollen morphology and wall structure (Yatskievych and Zavada 1984), and a