Flowering phenology of some native perennial tropical grasses from north‐eastern Australia

The division of north‐eastern Australia into tropical and sub‐tropical zones at approximately the latitude of 20° S, as suggested by the flowering phenology of Heteropogon contortus, is supported by studies on other perennial grasses of the native pastures. A progressive evolution away from an obligate short‐day flowering response which characterizes the tropical forms of Bothriochloa bladhii, perhaps Themeda australis, and the exclusive tropical species Dicanthium tenuiculum, through a quantitative short‐day response, as in the more widely distributed B. decipiens var. cloncurrensis, to the day‐neutral or opportunistic and largely subtropical species of B. decipiens and D. sericeum, is suggested as a sequence of flowering strategies leading to wider adaptation into the sub‐tropics. There is evidence from here and elsewhere that tropical forms or species of perennial grasses are grosser than their subtropical counterparts and this is coupled with their short‐day flowering behaviour. The evidence suggests that B. decipiens and D. sericeum are the evolutionary products of taxa nearer to B. decipiens var. cloncurrensis and D. tenuiculum which exhibit day‐length control of flowering.