Variation and Hybridization in Juniperus

The single species in the section CARYOCEDRUS, Juniperus drupacea, may герresent a relatively unsuccessful attempt at evolution toward a woody-coned form in this predominantly sclerophyllous and xeromorphic genus, or it may represent the sole surviving species of a more ancient group of junipers.This species is confined to the eastern part of the Mediterranean region.There are approximately ten species in the section oxycEDRUS, one of which, Juniperus communis, is circumboreal.Seven species are found in eastern Asia (China, Japan, Korea), a Pacific perimeter distribution, and two have a Mediterranean coastal distribution but extending through Persia to the Caucasus.The species of this section are characterized by acicular leaves as in CARYOCEDRUS, but they have fleshy berry-cones which are usually close to a centimeter in diameter, intermediate between the twice larger cones of CARYOCEDRUS and the generally small ones of SABINA.The sABINA section is much the largest, containing approximately thirty species.The majority of these are found in the more mesic habitats within and at the edges of the North American deserts.In the Old World about ten species are found from the Mediterranean to the Himalayas, China, and Japan.Subdivision of the sections becomes a rather arbitrary matter since the constituent species are all relatively similar morphologically.However, one character is available which clearly separates the species of the SABINA section into two groups.This character is the presence or absence of teeth-like processes on the margins of the leaf-single cells which project out from the other marginal cells at uniform intervals.The more mesic species, Juniperus barbadensis, J. virginiana, J. scopulorum, J. borizontalis, and J. Sabina, have entire margins while the more xeric ones, J. californica, P. pachyphloea, J. occidentalis, J. monosperma, J. Pinchoti, and J. Ashei, make a well-marked series from californica with very large teeth, to Ashei with relatively small ones.The species discussed in this study include five of those which occur east of the Rocky Mountains.One of these (Juniperus Ashei) is a member of the species group with denticulately fringed leaf margins, while the other four (barbadensis, virginiana, horizontalis, and scopulorum) are generally more mesic and are in the species group with entire leaf margins.Population studies have been made for three of them in regions where each meets Juniperus virginiana.Fassett (1944-45) made studies of populations showing introgression between J. scopulorum and J. virginiana.The data for Ashei and virginiana are presented in this paper.A key to all native species of the saBINA section adjacent to or overlapping the range of Juniperus Ashei and J. virginiana follows.It was made up from the examination of many specimens, and yet it combines elements of keys from Rehder (1940), Fassett (1945), and Hall (1947).This key is not constructed for the purpose of differentiating every variant, whether sport or hybrid, but expresses the fundamental differences between the species.For example, Juniperus virginiana L. var.ambigens Fassett is a trailing to semi-upright shrub generally with the habit of J. borizontalis but with the tech-[Vor.39 6