Cytogenetic Diversity in Scilloideae (Asparagaceae): a Comprehensive Recollection and Exploration of Karyo-Evolutionary Trends

The family Asparagaceae (subfamily Scilloideae, APG III, Botanical Journal of the Linnean Society 161:105–121, 2009 ) constitutes approximately 1000 species in about 33 genera of deciduous bulbous geophytes with long history of medicinal utilities. However, satisfactory delimitation of genera as well as species boundaries within most genera still remain doubtful for the lack of reliable discriminating characters with morphological traits showing continuous variation. Detailed cytogenetic characterization and thorough comparative analysis is still scanty in this group and thus can provide supportive taxonomical data besides serving as basis for further genomic studies. This group showcases diverse cytogenetic characters studied across 4 tribes: Hyacintheae, Urgineeae, Ornithogaleae and Oziroëeae. Cytogenetic investigation has not yet been initiated in more than 50% of accepted species, studies mostly limited to chromosome counts or conventional karyotyping methods. Somatic chromosome counts have been reported in around 378 species varying from 2n = 4 in Ornithogaleae to 2n = 150 in Hyacintheae and the basic ancestral chromosome number of x = 10 is proposed for the subfamily and secondary base numbers presumed to arise by descending dysploidy followed by polyploidization leading to such variation. Meiotic analysis and genome size estimation is reported in very few species and requires further investigation. Karyotype in most taxa exhibits a general pattern characterized by asymmetry with predominance of acrocentric chromosomes. Fluorochrome banding by CMA/DAPI staining and FISH although reported in very few species revealed characteristic patterns in different taxa, with potential taxonomic utilities. Thus, comparison of compiled data depicted some patterns of chromosomal diversity within the subfamily Scilloideae but study of more taxa is required for prediction of trends.