Feild, Taylor S., Franks, Peter J., and Sage, Tammy L. (2003) Ecophysiological shade adaptation in the basal angiosperm, Austrobaileya scandens (Austrobaileyaceae). International Journal of Plant Sciences, 164 (2). pp. 313-324.

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Abstract

Austrobaileya scandens, the sole species of the family Austrobaileyaceae, has been the subject of renewed interest following its placement near the root of the extant angiosperm phylogenetic tree. We present field observations on the growth habit, leaf anatomy, and physiological performance (photosynthesis and stem xylem hydraulics) of Austrobaileya from a premontane rain forest in northern Queensland. Austrobaileya scandens appears to possess functional characters that are commonly associated with flowering plants and ferns adapted to low light, including absence of palisade mesophyll tissue, low leaf photosynthetic rates, and possibly strong reliance on vegetative reproduction for recruitment. Also in line with many but not all shade-tolerant species, the photosynthetic apparatus of A. scandens expressed little physiological ability to upregulate CO2 assimilation rate to increased light availability under greenhouse conditions. Broadly, these features appear to contribute to increasing the collection of light for photosynthesis under light-limiting conditions and the establishment and persistence in forest understory habitats. The ecology and physiology of A. scandens is different from hypotheses that the earliest angiosperms were early-successional xeric shrubs, disturbance-loving herbs characterized by high capacity for photosynthesis and water transport, or aquatic herbs. Our observations of A. scandens, in the context of other early-diverging lineages of flowering plants, indicate that first angio-sperms were woody plants that exploited wet, relatively dark and disturbed (albeit at small scales) habitats.

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