ABSTRACT
Although tropical grasses are grown as warm-season grasses in temperate regions, these grasses are native to tropical regions and were originally grown in these areas. Since the 1920s, several superior lines and numerous native accessions of tropical grasses have been introduced into temperate regions and used intensely in these areas; thus, the term “warm-season grass” might be preferable for these “tropical” grasses. On the other hand, in tropical regions, the needs of animal livestock and husbandry have rapidly increased along with increases in economic development, and the forage use of tropical grasses is becoming more important in these areas. For this reason, we have retained the original term “tropical grass” rather than “warm-season grass”. The grass family (Poaceae) has been estimated to have evolved from taxa in the tropics and subtropics about 50 to 60 million years ago (Mya) based on fossilized grass spikelets and infl orescence fragments containing pollen (Crepet and Feldman 1991), and 100 to 115 Mya based on chloroplast genome sequences (Chaw et al. 2004). The extant tropical grasses have C4 photosynthesis mechanisms, and this system developed about 50 Mya, based on the time of appearance of the genes responsible for C4 photosynthesis (Giussani et al. 2001; Edwards and Still 2008); thus, the progenitor of the tropical grasses appeared 50 Mya. A total of 372 genera of tropical grasses have a C4 photosynthesis system, which is much more prevalent in tropical grasses than in other plant species; for example, all of the species of subfamily Chlorideae of tropical grasses exhibit C4 photosynthesis (Sage 2001).
