Are the male reproductive units of Juniperus drupacea Labill. (Cupressaceae s.str.) a compound, polyaxial inflorescence or a dense cluster of simple, uniaxial pollen cones?

Abstract

The Juniperus Section Caryocedrus (Cupressaceae) is one of the three putatively monophyletic sections of the genus. It is monotypic, presented only by J. drupacea. Male reproductive units of this species show several distinct features distinguishing it distinctly from all other Juniperus species, including an inflorescence‐like arrangement of pollen cones, an increased number of microsporangia per microsporangiophore, and microsporangia attached to the stalk in up to three subsequent rows. The male reproductive units in J. drupacea have been investigated with paraffin technique and SEM. They are hypothesized to represent a distal cluster of densely arranged, simple pollen cones, which are interpreted as being derived from an ancestral condition that is still presented in species of the Section Juniperus. This is assumed to have occurred by a profound reduction of internodes of the fertile shoot axis carrying the pollen cone and a distal shift. The increased number of microsporangia per microsporangiophore may be a response to the decreasing number of pollen cones per tree compensating for the loss of pollen, that occurred during the evolution of inflorescence‐like male reproductive units.