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Scanning electron microscopy examination of Texas specimens of Isoetes revealed differences in megaspore ornamentation patterns of the proximal and distal surfaces that support the recognition of four species of the genus in Texas. These include I. butleri and I. melanopoda, both of widespread occurrence in the central United States, I. lithophila, a central Texas endemic, and I. piedmontana, which we report as new to the state. A key to species based upon megaspore characteristics, distributions, a limited list of exsiccate, and descriptions and micrographs of megaspores are included.
In 1946 the Teucrium cubense complex was treated as having four subspecies by McClintock and Epling. In the present account these have been treated as distinct species: Teucrium cordobense, T. cubense, T. depressum, and T. laevigatum. An additional species, T. coahuilanum, is described from north-central Mexico, this previously recognized as a North American populational element of T. laevigatum.
A new species of Croton sect. Eluteria from Estado de Veracruz, Mexico, Croton gomezii, is described and illustrated. The species appears most closely related to Croton arboreus on the basis of its indumentum, but has been generally confused with Croton reflexifolius. A key is provided to aid in distinguishing Croton gomezii from related Mexican species of section Eluteria.
Two new species of Polygala subgenus Polygala (Polygalaceae) are described from western Mexico. Polygala mcvaughii is related to P. subalata, from which it differs by its shorter, broader racemes, longer pedicels, and always annual habit, and to P. conferta, differing from that species by its larger seeds and larger, usually ± non-stipitate fruits. It is known from 1200–2250 m in Michoacan, Jalisco, Aguascalientes, and extreme southern Zacatecas. Polygala tellezii belongs to a group of species in which a reduced or no aril and short seed hairs are the norm, and in which a vegetative vestiture of minute capitate hairs is common. This new species is in some ways morphologically most similar to the South American P. exigua, but it is perhaps most closely related to the sympatric P. glochidiata, from which it differs in its entirely alternate leaves and non-uncinate seed hairs. Polygala tellezii is known only from three localities in lowland savannas in southern Nayarit.
Hymenoxys subg. Rydbergia comprises H. brandegeei, H. grandiflora, and H. insignis. The treatment includes a discussion of the original circumscription of the taxa, the description of the genus Rydbergia to accommodate H. brandegeei and H. grandiflora, the eventual placement of Rydbergia within Hymenoxys as a subgenus, and relationships of the three taxa to one another and to other taxa of Hymenoxys. The treatment also includes synonymies, descriptions, and range maps for each of the species, and lectotypification of Actinella brandegeei.