Idiosyncratic phenomenon of regeneration from cotyledons in the idiot fruit tree, Idiospermum australiense

Idiospermum australiense (Diels) S. T. Blake, is a rare species that produc es very large diaspores (up to 225 g) comprising 2-6 cotyledons. Anecdotal evidence suggested that each cotyledon within the diaspore could develop an independent root/shoot axis in natural populations and under glasshouse co nditions. To investigate this potential, 13 diaspores were collected. Six d iaspores were kept intact and cotyledons in the remaining seven were separa ted, planted into soil and scored for germination. All shoots were allowed to grow for 12 weeks. To test for differences in growth response from seedl ings emerging from intact diaspores and single cotyledons, plant height, sh oot mass, stem mass, leaf mass and total leaf area were compared between gr oups using both absolute values and values standardized to initial reserve mass. To examine the effects of reserve mass in more detail, height to stem mass, leaf mass to stem mass and specific leaf area was also compared betw een groups. All intact cotyledons and 24 of the 27 single cotyledons produc ed a functional root/shoot system. Time to germination was not different be tween groups. Shoot mass, stem mass and leaf mass were significantly greate r in intact diaspores than in single cotyledons, although no difference was found in any parameter when standardized to initial reserve mass. Shoots a rising from individual cotyledons were significantly taller per gram initia l weight, because of a significantly greater relationship between height an d stem mass. Shoots arising from single cotyledons also had a significantly greater investment in leaf mass per unit stem mass, even though there was no difference in specific leaf area between groups. Thus, seedlings arising from individual cotyledons grew relatively taller and produced a greater a rea of leaf tissue relative to stem than those arising from intact diaspore s.