Infructescence and samara morphometrics and potential mechanism of samara release in Allocasuarina and Casuarina (Casuarinaceae)
Ian T. Riley
Department of Plant Production and Technologies, Faculty of Agricultural Science and Technologies, Niğde Omer Halisdemir University, TR-51240, Niğde, Turkey. Email: ian@riley.asia
Australian Journal of Botany 68(2) 108-118 https://doi.org/10.1071/BT19153
Submitted: 19 September 2019 Accepted: 17 March 2020 Published: 7 May 2020
Abstract
In addition to samara aerodynamics, mechanisms of samara release will contribute to seed dispersal outcomes. Analysis of species descriptions of Australian members of the Casuarinaceae (sheoaks) indicated cone shrinkage to be a possible mechanism enhancing samara release. However, measurement of cones of nine species of Allocasuarina and Casuarina did not support this hypothesis, but outward movement of samaras both in the field and in oven-dried cones indicated that another mechanism was operating. Microscopic examination revealed that the proximal margins of the bracteoles are involute after drying, and it is postulated that incurving of the bracteoles during drying moves samaras outward against gravity enhancing samara release. This study also revealed inconsistencies in cone and samara metrics between field samples (1–3 specimens for 9 species) and the published descriptions. This could lead to identification uncertainties, and indicates the need to revise the descriptions to more fully encompass the variation in sheoaks across their natural and anthropogenic ranges.
Additional keywords: anemochory, diaspore release, mechanism, seed dispersal, wind dispersal.
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