Seedling Morphology of some selected members of Commelinaceae and its bearing in taxonomic studies

Abstract

Seedling morphology of eight species from four genera of the family Commelinaceae viz. Commelina appendiculata C.B. Clarke, C. benghalensis L., C. caroliniana Walter, C. paludosa Blume, Cyanotis axillaris (L.) D. Don ex Sweet, C. cristata (L.) D. Don, Murdannia nudiflora (L.) Brenan and Tradescantia spathacea Sw. are investigated using both light and scanning electron microscopy. The seedling morphological features explored include germination pattern, seed shape, surface and hilum, root system, cotyledon type, cotyledonary hyperphyll (apocole), cotyledonary hypophyll (cotyledonary sheath), hypocotyl, first leaf and subsequent leaves. All taxa studied had hypogeal and remote tubular cotyledons. However, differences in cotyledon structure (apocole, cotyledonary sheath), seed, hypocotyl, internodes, first leaf and subsequent leaves were observed. Variations of those characters were used to prepare an identification key for the investigated taxa. Commelina spp. and Murdannia nudiflora of the tribe Commelineae were found to differ from Cyanotis spp. and Tradescantia spathacea of tribe Tradescantieae in the petiolate first leaf with papillate margins on upper surface with 6-celled stomata and the glabrous epicotyl. The presence of an elongated cotyledonary sheath, long apocole and extended periblast region appear to be synapomorphies for Commelina spp. and T. spathacea. The affinity of the investigated taxa as revealed through multivariate analysis supports some of the relationships inferred by pollen morphology, floral morphology and DNA (rbc-L, 5S NTS, trnL-trnF) data stated by previous authors.