Megaspores and microspores of forty-six species and a presumed hybrid of heterophyllous Selaginellae from Mexico and Central America are described. Characters of the spores are correlated with three major groupings-the group, the non-articulate group, and, within the latter, the group containing those species which curl into a ball when dried. A key based on spore and sporangial characters is included. The genus Selaginella has attracted much attention from morphologists because of its heterospory, its stelar anatomy, and its controversial organ, the rhizophore. The genus is nearly worldwide in distribution, although most of the species are tropical. Selaginella is generally divided into two subgenera: homophyllous species are placed in subgenus Selaginella; heterophyllous species (having two dorsal rows of smaller leaves and two lateral rows of larger leaves) are placed in subgenus Stachygynandrum. The latter has been further divided on the basis of habit, articulation of the stems, arrangement of the leaves, and geographical distribution (Greville & Hooker, 1831; Spring, 1850; Braun, 1860; Baker, 1883; Hieronymus, 1902; Alston, 1955). Stem articulation in Selaginella is presumed rather than real. At each node (site of stem ramification) in the articulate species there is a narrow constriction or discoloration of the main stem that is suggestive of an abscission layer. Alston (1955) prepared a key to the heterophyllous species of Selaginella of North America south to Panama. He grouped the species largely according to the characters used in previous classifications but occasionally made use of spore characteristics to separate difficult groups. The spore characters he used are color of both megaspores and microspores and ornamentation of the microspores. Tryon (1949) described the spores of the American species of Selaginella which occur north of Mexico. These are largely homophyllous species. Unpublished work by Mickel shows that the heterophyllous Selaginellae, which are mostly tropical, are more diverse in spore morphology than the homophyllous species. The present study describes the spores of the heterophyllous species of Mexico and Central America, especially with regard to color, size, and ornamentation. This information will be correlated with previous taxonomic groupings. This study is preliminary in nature and will undoubtedly be corrected and amplified by further investigation of this group. 1Based on a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, Iowa State University, Ames, Iowa. I thank Dr. John T. Mickel for pointing out the problem and for his assistance in the course of the study. 2Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50010. Present address: New York Botanical Garden, Bronx, New York 10458. ANN. MISSOURI BOT. GARD. 56: 444-464. 1969. This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 04:41:54 UTC All use subject to http://about.jstor.org/terms