PALYNOLOGICAL STUDIES OF GAYA AND HERISSANTIA (MALVACEAE)

This study compares Herissantia tiubae with 10 species of Gaya H.B.K., and Herissantia Medicus. The pollen morphology of the eleven species is described in detail by observations from both the scanning electron and light microscopes. The palynological data were used to produce pollen descriptions and a phenogram based on similarity coefficients. This information was combined with morphological and cytological data to determine the taxonomic relationship and proper placement of H. tiubae, which has the pollen characteristics of Herissantia and is properly placed in that genus. THE small American genera Gaya H.B.K. and Herissantia Medicus are generally well distinguished in morphological characters, especially those of the fruit (Fig. 1). In addition, chromosome numbers in Gaya have been reported for seven species, all of which have 2n = 12 (Krapovickas, 1957, 1967; Krapovickas et al., 1974; Bates, 1976); in contrast, Herissantia crispa, the commonest, most widely distributed species of Herissantia, has the chromosome number of 2n = 14 (Bates, 1976). A problem of delimitation of these two genera has arisen, however, in spite of these clear differences in modal expression. The problem arises from two facts: (1) the recent discovery of a species of Gaya, G. elingulata Krapovickas et al., that lacks the endoglossum characteristic of the genus but has the chromosome number 2n = 12 (Krapovickas et al., 1974), and (2) the report of 2n = 12 for Herissantia tiubae (Bates, 1976), a species generally regarded on morphological grounds as being properly placed in Herissantia. Krapovickas et al. (1974) have presented strong arguments for placing G. elingulata in Gaya, which we accept. The placement of H. tiubae, however, seems to be problematical, and the placement of the generic boundary is therefore in doubt. Three possible resolutions of this question present themselves: (1) Herissantia tiubae should be retained in Herissantia, and this genus should be accepted as polymorphic in chromosome number; (2) H. tiubae should be transferred to Gaya to make the genera cytologically homogeneous, in spite of the superficial resemblance of this species to others of Herissantia; or (3) the two genera are not distinct and should be merged into a single genus. I Received for publication 7 August 1978; revision accepted 17 January 1979. A resolution of this problem is to be sought in the evaluation of additional characters; palynological characters were singled out as possibly providing the evidence required. Previous work (Chaudhuri, 1965; Hashmi, 1970; Krapovickas et al., 1974) has indicated that pollen grains of Gaya, relative to Herissantia, are larger, have longer spines, and have more numerous apertures (ca. 25 vs. 3 or 4). This paper reports a palynological study of Herissantia tiubae compared to other species of Herissantia and Gaya. MATERIALS AND METHODS-The samples studied are identified in Table 1. Pollen grains extracted from these specimens were processed for study in the light microscope (LM) and scanning electron microscope (SEM) in the following way. All pollen samples of species to be observed with the light microscope were acetolyzed. The pollen grains were first boiled in 10%c KOH for 5 min, sieved, and then washed. After deflocculation, the grains were placed in an acetolysis mixture of acetic anhydride and H2SO4 (9:1) and boiled for 1 min (Faegri and Iverson, 1964). After the removal of the organic deposits by acetolyzation, the grains were washed and mounted on glass slides in glycerol jelly. The material was observed with a phase contrast Zeiss Opton2 microscope with a lOx eyepiece containing a calibrated micrometer, and measurements were obtained under 30x (oil immersion) and 100x (oil immersion) magnification. 2 Disclaimer. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.