Journal de Morphologie et d'Anatomie

Morphology of Juniperus Cone and its Implications on Cone Evolution

Abstract

Xin Wang and Xiuping Xu

Background:The basic cone unit in Pinaceaeis called Bract-Scale-Seed Complex (BSSC), in which the scale is supposed to be equivalent to an axillary shoot bearing ovules in Cordaitales. This correlation established by Florin provides a rational foundation on which an interpretation for the origin of cones in at least most Coniferalesis built, and may be called Florin model for convenience. Cupressaceaeis a family in Coniferales, in which the ovule-scale and its subtending bract are thought fully fused and hard to distinguish by external morphology.

Results: Different from Pinaceaeand other typical conifers, Juniperus(Cupressaceae)appears not following Florin’s model closely. For example, the cone of Juniperusoxycedrushas only three rather than more BSSCs in a whorl, and its fleshy fructification appears more like a berry rather than a typical coniferalean cone. In this paper morphology and anatomy of Juniperusoxycedrusfructifications are documented using Micro CT. New observation demonstrates clearly that three seeds alternate the three surrounding bracts in Juniperusoxycedrus.

Conclusion:Such spatial arrangement is quite different from that in typical BSSCs, in which the ovules should be aligned with their subtending bract. Together with other unexpected features in other cupressaceous cones, Juniperusmay help to expand the avenue through which we can interpret the origin and homology of cones in Cupressaceaeand other conifers or gymnosperms in general.