Germination behaviour of Astroloma xerophyllum (Ericaceae), a species with woody indehiscent endocarps

The dispersal unit of many Ericaceae comprises an ovoid drupe with a woody indehiscent endocarp, and diasporesof this type are notoriously difficult to germinate for most members of this widely distributed family. Within thebiodiverse south-west of Western Australia, more than 200 drupaceous species of Ericaceae have been described,more than 50 of which are considered to be rare and threatened, requiring significant conservation action in thenear future. In this paper, we investigate the germination ecology of the common Australian endemic, Astrolomaxerophyllum, as a proxy for closely related threatened taxa, focusing on the ex situ and in situ germinationrequirements of seeds and indehiscent endocarps. Each endocarp possessed up to seven locules and means of2.0–3.4 seeds per endocarp from the two collections used in this study. Seeds were up to 2.74 mm in length and100% viable. Embryos were linear, differentiated and approximately 1.3 mm in length. Seeds within endocarpsimbibed water to 28%, whereas excised seeds became hydrated to 44%. Fifty-five per cent of seeds extracted fromendocarps germinated on water agar alone and 100% germinated when presoaked in gibberellic acid. Seedsremaining inside intact endocarps failed to germinate unless treated with a germination promoter and incubatedfor more than 20 weeks. Rapid germination of seeds in intact endocarps was promoted by soaking endocarps ingibberellic acid and incubating them in 100% O2. Embryos grew substantially in length within seeds prior togermination, and thus seeds have morphophysiological dormancy. Seeds under natural conditions required severalseasons to germinate to any degree. © 2009 The Linnean Society of London, Botanical Journal of the LinneanSociety, 2009, 160, 299–311.