Tetratheca juncea Smith (Tremandraceae) has undergone a range contraction of approx. 50 km in the last 100 years and is now listed as a vulnerable sub-shrub restricted to the central and north coast regions of New South Wales, Australia. There are approx. 250 populations in a 110 km north±south distribution and populations are usually small with fewer than 50 plants/clumps. The reproductive ecology of the species was studied to determine why seed-set is reportedly rare. Flowers are bisexual, odourless, and nectarless. Flowers are presented dependently and there are eight stamens recurved around the pistil. Anthers are poricidal, contain viable pollen, and basally contain a deep-red tapetal ¯uid that is slightly oily. Thus ¯owers are presented for buzz pollinators, although none were observed at ¯owers during our study. The species was found to be facultatively xenogamous with only one in 50 glasshouse ¯owers setting seed autogamously, i.e. without pollinator assistance. Field studies revealed fertile fruit in 24 populations but production varied significantly across sites from exceedingly low (0´6 fruits per plant clump) to low (17 fruits per plant clump). Fruit-set ranged from 0 to 65 %, suggesting that pollen vectors exist or that autogamy levels in the field are variable and higher than glasshouse results. Fruit production did not vary with population size, although in three of the five populations in the southwest region more than twice as much fruit was produced as in populations elsewhere. A moderately strong relationship between foliage volume and fruit: ¯ower ratios suggests that bigger plants may be more attractive than smaller plants to pollinators. A review of Tetratheca pollination ecology revealed that several species are poorly fecund and pollinators are rare. The habitat requirements for Tetratheca, a genus of many rare and threatened species, are discussed.
Floral structure, breeding system and fruit-set in the threatened sub-shrub Tetratheca Juncea Smith (Tremandraceae)
Year: 2003
