The genus Lolium (Fig. 2-8) contains grasses recognized for their high productivity, persistence, nutritional content, and ability to adapt to a variety of environmental conditions (Jauhar, 1993). Consequently, many species within this genus are utilized for both agricultural and recreational (see Chapter 26) purposes, as well as for their environmental role of stabilizing soils (see Chapter 27 and Chapter 28). Traditional defining morphological characters are: leaves with falcate auricles; raceme with spikelets (Fig. 2-9) in two opposite rows edgeways on the rachis; spikelets several to many flowered; lower glume absent (except terminal spikelet); upper glume abaxial, shorter than lemma to as long as spikelet, coriaceous; lemma membranous to coriaceous, with or without a subterminal awn; hilium linear.
The classification of Lolium grasses has long been a source of contention. On the basis of its spike-like inflorescence structure, early researchers placed the genus Lolium in the grass tribe Triticeae (reviewed in Darbyshire, 1993). However, accumulating evidence based on hybridization and cytology (Jenkin, 1959), endosperm structure (Tateoka, 1962), serology (Butkute and Konarev, 1980), chloroplast DNA restriction sites (Soreng et al., 1990), thermal denaturation of genomic DNA (King and Ingrouille, 1987), and sequence-based phylogenies (Catalán et al., 1997; Mathews et al., 2000; Soreng and Davis, 1998) have supported placement of the genus Lolium together with Festuca in the tribe Poeae. In the course of grass evolution, spike and panicle forms of grass inflorescences have frequently arisen from each other, so gross inflorescence morphology is particularly unreliable for identifying major evolutionary relationships. Although the difference between a fescue panicle and the ryegrass spike seems dramatic to the specialist's eye, a more scientific classification system should emphasize more evolutionarily relevant characters and genetic relationships.
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Fig. 2-8. Lolium perenne (perennial ryegrass).
Fig. 2-9. Spike inflorescence of L. perenne.
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