Abstract
Tree euphorbias share many traits with arborescent cacti in having tall and multi-branched forms of growth which have selective value for maximizing photosynthetic surface area and water storage. The candelabra growth form of Euphorbia cooperi, and likely other Euphorbia species with similar canopy architecture in southern Africa, allows these plants to add photosynthetic surface area as they grow and increase in size while at the same time minimizing problems of transpirational water loss. This increase in branch surface area occurs with age and increase in size and numbers of branches at the same time that the amount of potential storage volume to support water loss from this expanded surface area is also increasing. Key to this ability is the morphological trait of a heavily suberized trunk that increases with age, providing added capacity for water storage without adding to surface area subject to transpirational water loss. This trait and the associated canopy architecture allows the development of increasing surface area with minimal self-shading as new branches develop so long as older branches are shed. Beyond the canopy architecture, the cross-sectional morphology of branches in E. cooperi with concave faces has selective value in balancing increased surface area with maintenance of adequate storage volume. Simulated patterns of branch morphology with a square cross-sectional morphology show a “safe” result in producing little change in S:V ratio as plants mature, but at the expense of limiting photosynthetic surface area. At the other extreme, a simulated cross-sectional morphology with deep concave flutes, as seen in young plants, would significantly increase photosynthetic surface area, but at a potential cost of increased sensitivity to drought stress.
Highlights
Much has been written about the growth form of arborescent cacti in the Southwestern United States and Mexico, with a particular emphasis on the significance of branching architecture on photosynthesis, water storage and its conservation, and reproductive success (Yeaton et al, 1980; Cody, 1984; Geller and Nobel, 1986, 1987; Drezner, 2003)
Through simulations of two hypothetical variants in branch perimeter ratio, we examine the consequences of cross-sectional shape on photosynthetic surface area and volume available for water storage
Height to branching in the sampled population of Euphorbia cooperi ranged from 1 m to 8.5 m, with a mean height of 3.9 m
Summary
Much has been written about the growth form of arborescent cacti in the Southwestern United States and Mexico, with a particular emphasis on the significance of branching architecture on photosynthesis, water storage and its conservation, and reproductive success (Yeaton et al, 1980; Cody, 1984; Geller and Nobel, 1986, 1987; Drezner, 2003). A diverse set of arborescent euphorbias occurs with a wide range of distribution across southern and eastern Africa and extending to the Arabian Peninsula and across the continent to Southeast Asia (White et al, 1941). Such growth forms and the associated succulence with crassulacean acid metabolism (CAM) have evolved multiple times within the genus and stimulated diversification in these lineages (Bruyns et al, 2011; Evans et al, 2014; Horn et al, 2014). A.; Schmidt et al, 2002)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
