POLLEN MORPHOLOGY AND SYSTEMATIC RELATIONSHIPS AMONG NEW WORLD SPECIES IN TRIBE ANTIRRHINEAE (SCROPHULARIACEAE)

The morphology of mature pollen grains among 12 New World genera in tribe Antirrhineae has been examined with light and scanning electron microscopy. Pollen from 29 American species have mean polar diam that range from 17 to 26 ,um, have a tectate structure with perforate, microreticulate, or reticulate surface pattern, and are subspheroidal to prolate, and trizonocolporate with fusiform or narrowly oblong colpi that are free or occasionally fused at the poles. Among the genera, pollen size is positively associated with style length but not haploid chromosome number. Three major morphological categories are recognized based on grain shape, exine structural pattern, and colpus shape. Two of these morphotypes each characterize individual genera (Mohavea, Linaria). The other morphological category includes ten New World genera and has been divided into three subcategories based on variation in lumina diam and intermittent occurrence of fused colpi. Only Antirrhinum and Pseudorontium have species or populations with pollen in more than one subcategory. Concordance of morphological, anatomical, chromosomal, and palynological data suggests that Linaria and Mohavea are best placed in separate subtribes from other native American genera. Compared to Old World taxa in tribe Antirrhineae, the most common pollen type (subspheroidal, microreticulate, apocolpate, fusiform colpi) may be the most primitive. Pollen grains with fused colpi (Antirrhinum p.p., Pseudorontium) and perforate (Mohavea) or reticulate (Holmgrenanthe) structural patterns probably represent derived types. THE APPROXIMATELY 12 native New World genera in tribe Antirrhineae have unresolved taxonomic and phylogenetic relationships. These problems are exemplified by different classifications of certain genera (Antirrhinum L., Galvezia Dombey ex Juss., Maurandya Ort.) and subtribes (Gambeliinae, Linariinae, Maurandyinae) presented by various workers (e.g., Wettstein, 1891; Rouy, 1909; Munz, 1926; Rothmaler, 1943, 1954, 1956; Elisens, 1985a). The New World taxa have several chromosome base numbers and polymorphic habit, leaf, calyx, corolla, fruit, and seed characters. The diversity, patterns, and gaps of these data have been discussed previously (e.g., Rothmaler, 1943; Elisens and Tomb, 1983; Elisens 1985a, 1985b). Within the tribe, there is a greater diversity of subtribes (four of five) and ' Received for publication 11 October 1985; revision accepted 7 March 1986. I am indebted to the following individuals who permitted access to SEM and photographic facilities at their institutions: A. S. Tomb at the Kansas Agricultural Experiment Station at Kansas State University, S. Meier at the University of Texas at Austin, and T. N. Taylor at the Ohio State University. I thank M. Kurmann and D. M. Spooner who provided helpful comments on an earlier draft of the manuscript. This material is based upon work supported by the National Science Foundation under grant BSR-8408026 awarded in 1984. genera (12 of 21) in the New World (sensu Rothmaler 1943, 1954), even though the American taxa are less speciose (40 to 50 species) than in the Old World (250 to 300 species). Only Antirrhinum and Linaria Mill. have indigenous species in both the Old and New World; Rothmaler (1954) placed these two genera, as well as Neogaerrhinum Rothm., Pseudorontium (A. Gray) Rothm., and four Old World genera in subtribe Linariinae. The remaining American genera have been included by Rothmaler (1 9 54) in the exclusively New World subtribes Gambeliinae (Galvezia, Gambelia Nutt., Saccularia Kellogg), Mohaveinae (Mohavea A. Gray), and Maurandyinae (Holmgrenanthe Elisens, Maurandya, Mabrya Elisens, Lophospermum D. Don; sensu Elisens, 1985a). Except for a synopsis of pollen morphology in subtribe Maurandyinae (Elisens, 1985a), a thorough investigation of systematic relationships based on pollen data has not been undertaken. Most previous reports of pollen size, aperture type, and surface pattern have been presented in comprehensive treatises (e.g., Fritsche, 1832; Hassell, 1842; Edgeworth, 1877; Faegri and Iversen, 1974), surveys of regional floras (e.g., Ikuse, 1956; Nair, 1965; Inceoglu and Karamustafa, 1977; Kuprianova and Al-