Isachne

Abstract: ISKANDAR, E.A.P. & VELDKAMP, J.F. 2004. A revision of Malesian Isachne sect. Isachne (Gramineae, Panicoideae, Isachneae). Reinwardtia 12 (2): 159 – 179. – There are ca. 23 species of Isachne in Malesia of which the seven belonging to sect. Isachne are treated here. Isachne miliacea Roth has been misapplied to I. minutula (Gaudich.) Kunth, as its type belongs to I. globosa (Thunb.) Kuntze. Isachne pulchella Roth is the correct name for I. dispar Trin.

Abstract: Gramineae is the fourth largest family of flowering plants, it has about 700 genera and 10,000 species in the world. Grasses are economically very important as major cereals like wheat, rice and maize are grasses, as are also the sugarcane and bamboos; they bind soil. Grasses provide variety of other useful products for food, fodder, oils, house-building, and for lawn making, etc. India has about 266 genera and 1200 species. The list of genera is appended. About 360 grass taxa are endemic to India. Rich diversity and endemism suggest that some grass genera, like Isachne, Dichenthium, Ischaemum, Dimeria and Arthraxon might have had their primary or secondary centre of origin in India. Several grasses are now rare and threatened. A list of about one hundred grasses which are endemic and also rare is appended. It is emphasized that revisionary studies on large genera are necessary for better, evaluation of diversity and endemism.

Abstract: Worldwide chromosome number information has been compiled from the literature for monocotyledonous genera whose members have been cytologically studied in the last three years from Kangra District (Himachal Pradesh) and Kashmir (Jammu & Kashmir) in the Western Himalayas, comprising 143 species of 86 genera in 12 families, many in the family Poaceae. Chromosome number information from the literature is supplemented with new and varied reports for 54 species/56 taxa from the present study. Overall, the chromosome numbers range from 2n=10 to 2n=120. Some species in all genera show a large number of cytotypes, clearly highlighting the role of inter- and intraspecific genetic diversity as well as polyploidy and dysploidy. The basic chromosome numbers in all 86 genera are reconsidered. Monobasic genera are more common in Poaceae, and polybasic genera are more common in the other 11 families. Polyploidy in the different genera ranges from 3x to 40x, and is quite high in certain genera (18x in Avena, Bothriochloa, Isachne, Helictotrichon and Panicum; 19x in Saccharum; 24x in Tradescantia; 28x in Eleocharis; 32x in Cyperus; 36x in Andropogon; 38x in Poa; 40x in Dioscorea). An updated checklist of chromosome number variability in these genera is given for India and worldwide.

Abstract: PREMISE OF THE STUDY We investigated the little-studied Arundinoideae/Micrairoideae clade of grasses with an innovative plastome phylogenomic approach. This method gives robust results for taxa of uncertain phylogenetic placement. Arundinoideae comprise ∼45 species, although historically was much larger. Arundinoideae is notable for the widely invasive Phragmites australis. Micrairoideae comprise nine genera and ∼200 species. Some are threatened with extinction, including Hubbardia, some Isachne spp., and Limnopoa. Two micrairoid genera, Eriachne and Pheidochloa, exhibit C4 photosynthesis in this otherwise C3 subfamily and represent an independent origin of the C4 pathway among grasses. METHODS Five new plastomes were sequenced with next-generation sequencing-by-synthesis methods. Plastomes were assembled by de novo methods and phylogenetically analyzed with eight other recently published arundinoid or micrairoid plastomes and 11 outgroup species. Stable carbon isotope ratios were determined for micrairoid and arundinoid species to investigate ambiguities in the proxy evidence for C4 photosynthesis. KEY RESULTS Phylogenomic analyses showed strong support for ingroup nodes in the Arundinoideae/Micrairoideae subtree, including a paraphyletic clade of Hubbardieae with Isachneae. Anatomical, biochemical, and positively selected sites data are ambiguous with regard to the photosynthetic pathways in Micrairoideae. Species of Hubbardia, Isachne, and Limnopoa were definitively shown by δ13C measurements to be C3 and Eriachne to be C4. CONCLUSIONS Our plastome phylogenomic analyses for Micrairoideae are the first phylogenetic results to indicate paraphyly between Isachneae and Hubbardieae. The definitive δ13C data for four genera of Micrairoideae indicates the breadth of variation possible in the proxy evidence for photosynthetic pathways of both C3 and C4 taxa.