Floral Structure, Breeding System and Fruit-set in the Threatened Sub-shrub Tetratheca juncea Smith (Tremandraceae)

Abstract

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 dependentally and there are eight stamens recurved around the pistil. Anthers are poricidal, contain viable pollen and basally contain a deep-red tapetal fluid that is slightly oily. Thus flowers are presented for buzz pollinators, although none were observed at flowers during our study. The species was found to be facultatively xenogamous with only one in 50 glasshouse flowers 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 south-west region more than twice as much fruit was produced as in populations elsewhere. A moderately strong relationship between foliage volume and fruit : flower 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, is discussed.

Reproduction of Amorpha canescens (Fabaceae) and diversity of its bee community in a fragmented landscape

“…Our results are in contrast to those of many studies that have shown negative eVects of remnant size on reproduction in small populations of native plants (Jennersten 1988;Aizen and Feinsinger 1994;Ågren 1996;Morgan 1999;Brys et al 2004), but are in agreement with others that have found no eVects or only intermittent eVects of size (Heschel and Paige 1995;Alexandersson and Ågren 1996;Molano-Flores and Hendrix 1999;Gross et al 2003).…”

Limited pollen-mediated dispersal and partial self-incompatibility in the rare ironstone endemic Tetratheca paynterae subsp. paynterae increase the risks associated with habitat loss

“…paynterae these extrinsic factors, together with partial self-incompatibility are likely to be more important in limiting selfing than physical features of the flower as suggested by Gross et al (2003) for the rare east coast endemic T. juncea. Pollination studies revealed T. juncea was self-compatible but preferentially outcrossing.…”

“…The numbers of flowers per treatment are listed in Table 1. The stigma in Tetratheca species is small (0.02 mm wide in T. juncea; Gross et al 2003) and pollen was therefore deposited, using a dissecting needle, on both the tip and sides of the style that were protruding from the anther whorl. A micro-dissecting head lens was used to check that pollen had been transferred.…”

“…Flowers produce no nectar and the sole reward for pollinators is pollen stored within anthers that open via apical pores. Based on observations that pollination events were rare in Tetratheca juncea in eastern Australia Gross et al (2003) suggested that Tetratheca species were particularly vulnerable to any disruption of pollination services. Species dependent on outcross pollen for fertilisation and on seed for reproduction are likely to be most vulnerable.…”

Reproductive ecology of medicinally important Kashmir Himalayan species of Digitalis L.

“…Reproductive ecology is of fundamental importance in determining the barriers to production of reproductive propagules and is of pivotal significance in formulating strategies for the conservation of taxa (Gross et al 2003;Tandon et al 2003), particularly with small population sizes . Because of unprecedented increases in anthropogenic causes of population decline, conservation biologists have extensively studied the effects of small population size on demography (Menges 1991), reproductive success (Young & Brown 1998) and genetic variation (Prober & Brown 1994).…”