Morphology of Juniperus Cone and Its Implications on Cone Evolution

Abstract Background The basic cone unit in Pinaceae is 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 Coniferales is built, and may be called Florin model for convenience. Cupressaceae is 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 Pinaceae and other typical conifers, Juniperus (Cupressaceae) appears not following Florin’s model closely. For example, the cone of Juniperus oxycedrus has 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 Juniperus oxycedrus fructifications are documented using Micro CT. New observation demonstrates clearly that three seeds alternate the three surrounding bracts in J. oxycedrus. Conclusions 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, Juniperus my help to expand the avenue through which we can interpret the origin and homology of cones in Cupressaceae and other conifers or gymnosperms in general.