Abstract Detail



Anatomy and Morphology

Huggett, Brett [1], Micklewhite, Niamh [2], Alison , Ricciardi [3], Tomlinson, P. [4].

Hydraulic architecture of the leaf axis in cycads.

The leaf axis of members of the order Cycadales (“cycads”) have arrangements of vascular bundles that in transverse section resemble the inverted Greek letter omega (hence the “omega pattern”). This arrangement provides useful diagnostic characteristics for the order, especially when applied to fossils. Using sequential serial images translated into cine format, we have provided a three-dimensional analysis of the vascular architecture of the pinnately compound leaf in Cycas revoluta. The omega pattern in the axis can be subdivided into three vascular components, an abaxial “circle”, a central “column” and two adaxial “wings”, the last being the only direct source of vascular supply to the leaflets. In this representative species, each leaflet is supplied by a single vascular bundle. There is neither multiplication nor anastomoses of vascular bundles in the other two components. Thus, as one proceeds from base to apex along the leaf axis, the number of vascular bundles in circle and column components is progressively reduced distally by their uniform migration throughout all components. Consequently, distal leaflets are irrigated by the more abaxial bundles, guaranteeing uniform water supply along the length of the axis. Hence the hydraulic architecture can be seen to be efficient. This very objective method has now being applied to examples from other genera, all of which differ from the very uniform arrangement in Cycas, in that each leaflet is now supplied by a series of vascular bundles, all still diverging from the wing bundles, but now with some anastomosing among column and circle bundles. This seems increasingly to obscure the omega pattern, but may introduce a more plastic and adaptive hydraulic architecture. Our goal is to complete a thorough analysis of the three-dimensional arrangement of the vascular networks in the entire order Cycadales, which then can be used to explore evolutionary trends and the possible links between hydraulic limitations and geographic distribution of particular taxa.


1 - Bates College, Biology, 44 Campus Ave, Lewiston , ME, 04240, United States
2 - Bates College, Biology, 44 Campus Ave., Lewiston, ME, 04240, USA
3 - Bates College, Biology, 44 Campus Ave., Lewiston, ME, 04240, United States
4 - Montgomery Botanical Center, 11901 Old Cutler Road, Coral Gables, FL, 33156, USA

Keywords:
Cycad
omega pattern
anatomy
xylem
hydraulic architecture.

Presentation Type: Oral Paper
Number:
Abstract ID:250
Candidate for Awards:None


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