REPRODUCTIVE-BIOLOGY OF RAVENALA-MADAGASCARIENSIS GMEL AS AN ALIEN SPECIES

The exotic arborescent monocot species from Madagascar, Ravenala madagascariensis, was studied in suburban gardens in Darwin, Australia. Inflorescences are long-lived branched spikes produced at right angles to a spectacular fan-like array of foliage. They are composed of a variable number of green boat-like bracts which contain a dilute liquid. Each bract subtends a series of individual, stiff, upright, large flowers which appear every 2.3 days, the total number of flowers being variable (up to 29). The slightly musty sweet smelling, creamy white hermaphrodite flowers, sometimes protogynous, opened at night (82.6% of flowers observed). Anthesis lasted, on average, 1.3 days and stigmas were receptive within the 24 hours of flower opening. Initially, nectar production was copious (1400 mul 12 hr-1) and concentration moderate (14.5% sucrose equivalents), but maximum production (1600 mul 12 hr-1) with slightly reduced concentration (12.5% sucrose) occurred at 2400 hr. Seed set occurs in Darwin plants, with the brown seed enveloped in a bright blue aril and displayed very obviously in the dehisced capsule. While autogamy treatments revealed that Ravenala is at least a facultative selfer, in Darwin the flowers were most frequently visited by the megachiropteran bat, Pteropus alecto gouldii, and only occasionally by the smaller bat, Macroglossur lagochilus, and honeyeater birds (Meliphagidae). Apart from reproducing vegetatively, the ability of Ravenala to set seed when grown outside its normal range in the absence of its co-evolved pollinator(s), either by selfing or by using a suitable indigenous pollinator, could allow the species to assume pest status in parts of the tropics where it is planted as an ornamental.