Morphological and molecular characterization of a new record of Isoëtes coromandelina subsp. coromandelina from Cambodia
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Plants of a heterosporous fern, Isoëtes, were collected from a wetland in Pu Rodet Leu, Mondulkiri, Cambodia, in which the flora has not yet been well studied. The characteristics of this quillwort, for example, dimorphic megaspores and small tuberculate ornamentation, were congruent with those of Isoëtes coromandelina L. f. subsp. coromandelina. Unlike most Isoëtes endemic species, this subspecies has a wide geographical range across India and the neighboring regions, and another subspecies, I. coromandelina subsp. macrotuberculata Marsden, grows in Australia. We have provided detailed characteristics for the first record of an Isoëtes species in Cambodia. Moreover, megaspore morphological features and the sequence of the chloroplast trnL intron were investigated to verify infraspecific and regional variation within this species, using specimens from India (Rajasthan and Varanasi), Sri Lanka, and Australia. Dimorphic megaspores were observed in similar proportions in a megasporangium of the Cambodian plant; the large spherical type averaged 378.5 μm in height in 409 megaspores, and the small flattened type averaged 227.7 μm in height in 544 megaspores. Microspores were not observed. The Cambodian Isoëtes plant is a tetrapolyploid (2n = 44 + 1). The morphological characteristics of the Cambodian quillwort are closer to those of a plant from Varanasi, India, than to those of plants from other regions in terms of tubercle size on the megaspore surface and polyploidy of chromosomes. Three haplotypes of the trnL intron showed regional specificity according to the country. However, the phylogenetic monophyly of all the plants examined was supported among the phylogeny of the entire Isoëtes genus. This close molecular relationship indicates that a recent dispersal of I. coromandelina may be related to its present distribution.
KeywordsIsoëtes coromandelina Cambodia Infraspecific variation Dimorphic megaspore trnL intron Dispersal
We thank Dr. Germinal Rouhan (Museum National d’Histoire Naturelle, P), Dr. Sarah Hirst (Department of Land Resource Management, DNA), and Dr. James C. Solomon (Missouri Botanical Garden, MO) for assistance in studying the specimens. The field collection by H. Won in Cambodia was supported by the National Institute of Biological Resources (NIBR), Ministry of Environment, South Korea. This study was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government [Ministry of Education, Science, and Technology (MEST)] (NRF-2011-0016929).
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