Morphological and molecular characterization of a new record of Isoëtes coromandelina subsp. coromandelina from Cambodia

Abstract

Plants of a heterosporous fern, Isoetes, 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 Isoetes coromandelina L. f. subsp. coromandelina. Unlike most Isoetes 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 Isoetes 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 Isoetes 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 Isoetes genus. This close molecular relationship indicates that a recent dispersal of I. coromandelina may be related to its present distribution.