R.P. Adams, webmaster
I suggest you visit it if you're looking for the most current info on any taxon in Juniperus.
Juniper, cedar, redcedar; cedro, sabino [Spanish] (Adams 1993).
This is the largest genus in the Cupressaceae in terms of species. In this treatment, there are 55 species:
The genus is characterized by fleshy cones with hard-shelled seeds, adaptations to avian seed dispersal; apart from this, all characters common to all of its species can also be found in other closely allied genera of Cupressaceae, notably Cupressus, Platycladus and Microbiota. About 50 species; this number is subject to revision as new taxa are identified and old ones are combined. Taxonomic work of this sort has become extensive in Juniperus since about 2001 as molecular taxonomic methods have been widely applied in the genus. The first such effort to include nearly all species in the genus was published by Mao et al. (2010) and is here described. This effort examined chloroplast DNA with some additional work using nuclear internal transcribed spacer DNA to check for congruency, which was generally well-supported.
The genus has traditionally been divided into three distinct sections or subgenera, sometimes treated as genera; descriptions of which are provided below:
The analysis by Mao et al. (2010) is summarized in the figure at right, which is derived from their (much more complex) Figure 2. Their analysis also included all species of Cupressus (sensu latu) and a variety of other Cupressaceae genera; see Cupressus and Chamaecyparis for discussion of those results.
In Juniperus all species were assigned to six major clades. All are individually well-supported, though some divisions within the clades are only weakly supported. The first clade to differentiate was that corresponding to sections Juniperus and Caryocedrus, shown here in magenta. Within this clade J. drupacea, the only species in section Caryocedrus, differentiated about 20 million years ago, with remaining speciation (section Juniperus) mostly occurring within the past 10 million years; this includes two well-supported subclades, the "blue seed cone" and "red seed cone" groups of Adams (2008). The remaining five clades represent the species of section Sabina and generally show a pattern of geographic differentiation. Clade I (green) contains species of the Himalaya and Tibetan Plateau. Clade II (red) contains the serrate-leaf-margin species of North America, widely recognized as a distinct subgroup. Clade III is mostly comprised of the smooth-leaf-margin American species, which are sister to three earlier-derived subclades containing the central Asian species J. sabina, J. semiglobosa and J. microsperma. Clade IV (brown) contains a far-flung mixture of European, Asian and African species, and Clade V (black) contains only J. phoenicia, native to the Mediterranean and the only serrate-leaf-margined Old World species. The sister relationship between Clades I and II is well-supported, but between this group and clades III, IV and V, relationships are unclear.
Fossil and molecular clock data presented by Mao et al. (2010) indicate that these major clades differentiated from Cupressus about 50-72 million years ago, during the Paleocene. Subsequent differentiation of the sections in Juniperus and clades in section Sabina occurred at about the time of the Eocene-Oligocene transition, between 30 and 50 million years ago. Disjunctions between Eurasian and North American species arose at three times: 30-43 million years ago during the Eocene-Oligocene transition, when Clade II (red) differentiated; 5-17 million years ago within Clade III (blue), and 0.3-4.6 million years ago within the Eurasian and North American varieties of J. communis.
These results are biogeographically plausible. The data presented by Mao et al. (2010) indicate that the common Cupressus-Juniperus ancestor was in Asia during the Cretaceous-Tertiary transition. Diversification of Juniperus sections occurred during Paleocene and Eocene time. A period of relatively rapid speciation apparently occurred during the cooling of the Eocene-Oligocene transition, at which time conifers showed substantial poleward range increases (Farjon 2005). Rapid speciation occurred again near the Oligocene-Miocene transition and again during the late Miocene through the Pliocene. These events also coincided with variable climate regimes, and also with the rise of the Qinghai-Tibetan Plateau in Asia and the development of the Basin & Range region in North America and the Central Volcanic Plateau in Mexico. These areas are all current hotspots of juniper diversity. On a global scale, the Pliocene was a period of cooling and drying, producing a rapid increase in the area of semiarid regions, juniper's principal habitat. J. communis, the most widespread of all junipers, favors wetter, cold habitats, which have become extremely widespread in the past 2 million years (the Pleistocene). The data presented by Mao et al. (2010) indicate that the radiation of this species has been relatively recent, within this time frame.
The dispersal of Juniperus is an interesting subject because it is a bird-dispersed genus and thus is much less affected by water or wind barriers that are most species of the Cupressaceae or Pinaceae. J. bermudiana (Clade III, blue) is endemic to Bermuda and appears to have arisen within the past 1 million years, and about the same time frame applies to J. saxicola of Cuba and J. barbadensis (J. lucayana in the cladogram) of Santa Lucia, Haiti, Jamaica and Cuba. Africa was an island when J. procera differentiated about 42 million years ago, and it is still the only juniper in sub-Saharan Africa.
Finally, Mao et al. (2010) note that ancestral Juniperus seem to have inhabited a warm climate with a distribution that coincided with the Madrean-Tethyan Flora of Axelrod (1975), a warm-dry sclerophyllous vegetation type located in the northern semiarid belt of the Eocene, which ran from California to Newfoundland to Spain to Iraq at a time when the Atlantic Ocean was still quite narrow. They suggest that the principal clades of section Sabina may have diverged within this vegetation type, subsequently going extinct in Europe during widespread late Tertiary extinctions in that region, while persisting in Asia and North America. Specifically, Clade II could have arisen in North America at this time, with Clade III later colonizing North America during Miocene time via the Bering Land Bridge.
Evergreen shrubs or trees. Branchlets terete, 4-6 angled, variously oriented, but not in flattened sprays (except in J. flaccida). Leaves in decussate (alternating) opposite pairs in 4 ranks or in alternating whorls of 3 in 6 ranks, rarely in whorls of 4 in 8 ranks. Adult leaves closely appressed to divergent, scalelike to subulate, free portion nil to 25 mm (to 32 mm recorded in J. formosana); abaxial gland visible or not, elongate to hemispheric (J. ashei), sometimes exuding white crystalline deposit. Pollen cones with 3-7 pairs or trios of sporophylls, each sporophyll with 2-8 pollen sacs. Seed cones maturing in 1 or 2 years, globose to ovoid and berrylike, 3-20 mm (to 25 mm in J. drupacea), remaining closed, often glaucous; scales persistent, 1-5 pairs or whorls of three, peltate or valvate, tightly coalesced and fused together, thick and fleshy or fibrous to obscurely woody; some sweet (e.g. J. deppeana), many bitter and/or resinous. Seeds 1-3 per scale, round to faceted, wingless; cotyledons 2-6. Seed dispersal by frugivorous birds, which swallow the cones whole, digest the fleshy scales and pass the hard-shelled seeds undamaged through the gut; the bitter taste of many species may be related to discouraging mammalian predators of the seeds. x = 11.
Leaves not decurrent down stem, with basal abscission zone; in six rows in alternating whorls of three, mostly of 1 kind, subulate, spreading, 5-25(32) mm long, 1-2 mm wide. Winter buds present. Scale-leaves absent, except for 2 (-3) whorls of three on the cone peduncles, and 1-2 (-3) whorls as bud scales on the winter buds. Dioecious, with male and female cones on different trees. Cones axillary on shoot, on a very short 0.3-1 mm peduncle (appearing sessile); peduncle scale-leaves 1 mm. Mature female cones small to medium, 6-15 mm, scales valvate in 1(-2) whorls of three, one whorl fertile, with 1 seed on each fertile scale, the three seeds not fused together; mature in c.18 months from pollination.
About 7-9 species; type J. communis L. The section is divisible into two subsections, a northern group with blue-black mature cones and one broad leaf stomatal band (J. communis and allies; 2-4 spp.), and a southern group with orange-red mature cones and two narrow leaf stomatal bands separated by the midrib (J. oxycedrus and allies; 5 spp.).
Leaves as in sect. Juniperus, including basal abscission zone, except broader (2-3.5 mm wide); 10-25 mm long. Winter buds present. Scale-leaves absent, except for 3-6 whorls of three on the cone peduncles, and 2-3 whorls as bud scales on the winter buds. Dioecious, with male and female cones on different trees. Cones axillary on shoot, on 2-7 mm peduncles; peduncle scale-leaves 1.5-3.5 mm long. Mature female cones large, 18-25 mm, scales valvate in (2-)3(-4) whorls of three, only one whorl fertile, with 1 seed on each fertile scale, the three seeds fused together in a hard bony-textured nut 10-12 mm long; mature in c.18 months from pollination. Type (and only species) J. drupacea Labill. The section is closely allied to sect. Juniperus and may be better treated as a subsection within it.
Leaves decurrent down stem, without basal abscission zone, in four rows in decussate opposite pairs or (occasionally) in six rows in alternating whorls of 3 or eight rows in alternating whorls of 4, of three kinds: scale-like adult leaves on slow-growing and fertile shoots, 1-2 mm, adpressed or with spreading apex, free portion 0-1 mm; whip leaves on strong-growing lead shoots, subulate, spreading, free portion 0.5-2 mm; and juvenile leaves, subulate, spreading, free portion 2-10(-13) mm. In all species, juvenile leaves are produced early in life and often also later on shaded shoots; in a few species (J. pingii, J. procumbens, J. recurva, J. squamata), juvenile-type leaves borne throughout life, with scale-leaves confined to cone peduncles. These and juvenile plants of other species may be distinguished from sect. Juniperus by the leaves being decurrent and lacking a basal abscission zone. Winter buds absent. Monoecious or dioecious, with male and female cones on the same or different trees depending on species. Cones terminal on 1-5(-20) mm scale-leaved side shoots. Mature female cones small to medium, 4-18(-20) mm, scales peltate in 2-4(-5) decussate pairs, 1-4(-6) scales fertile, with 1-3 seeds per fertile scale, the total 1-12+ seeds not fused together; mature in (4-)6-18 months (possibly longer in some spp.) from pollination. About 40 species; type J. sabina L. The section is divisible into several groups based on phenology, cone characteristics and leaf margin form; precise alliances are not yet determined.
Source: Adams (1993), M.P. Frankis personal observations).
Primarily Northern Hemisphere, one species (J. procera) in E Africa to 18°S. In many semiarid regions, such as through much of the western USA, northern Mexico and central & southwest Asia, it provides the dominant forest cover on large sections of the landscape. Sect. Juniperus is primarily Eurasian, with one species (J. communis) holarctic, the only member of the section in N. America and by far the most widespread single conifer species. Sect. Caryocedrus is a local endemic in SW Asia and SE Europe. Sect. Sabina occupies most of the range of the genus, except for Eurasia north of 50°N in Europe and 60°N in Asia.
The limited data I have found suggest it is J. occidentalis. Tallest may be J. drupacea, measured to c. 40 m tall in Turkey (H. Karaca).
Again, there are no data for most species, but ages of about 2000 years have been established for J. scopulorum.
A variety of species have proven useful, delivering dendroclimatic records of up to 1000 years and providing archeological data in the American southwest. However, some species lack circuit uniformity or have a large fraction of missing rings.
Numerous cultivars of Juniperus species are widely used for landscaping (Adams 1993). Because the genus is widely distributed in semiarid regions (it grows particularly well on calcareous soils) and some are not particularly palatable to domestic goats, it often affords the only tree of size on the landscape, thus providing an important source of wood for construction, fuel and other domestic uses. The wood is fragrant, usually reddish or reddish-brown, easily worked, very durable, and rarely injured by insects (Dallimore et al. 1967). Its resistance to decay makes it particularly useful for fenceposts and other ground-contact applications. However, it seldom achieves the size or straight grain needed in lumber. Many native peoples have used the aromatic foliage and resins for medicinal or spiritual purposes. "An essential oil is obtained by distillation from wood and leaves. That from the wood is often used for perfumery, sometimes in medicine. Oil from the leaves and shoots is also used in medicine. They have powerful diuretic properties and stock should not be allowed to eat branches" (Dallimore et al. 1967).
Wood and/or foliage are often burned for incense in Buddhist temples.
Cones of J. communis are used for flavouring gin.
See the respective species. Please inform me if you know of any arboreta with exceptional Juniperus collections.
Juniperus is an old Latin name used by Virgil and Pliny (Weber 1987).
"Mutants, or 'sports,' affecting plant habit and foliage are present in all species and are likely related to single-gene mutations. Many have been given formal names or incorrectly ascribed to hybridization. Gymnocarpy (bare seeds protruding from the cone), caused by insect larvae, is occasionally found in most junipers, particularly in the southwestern United States. Specimens with such aberrations may be almost impossible to identify without chemical data" (Adams 1993).
Juniperus is primarily dispersed by birds. As in most Podocarpaceae and Taxaceae, the female cone has been modified to resemble a fruit which appeals to birds and provides significant nutritional value, with the undigested (but somewhat scarified) seed excreted along with a measure of nitrogen that may help to nourish the seed. A few mammals, notably canids, and harvester ants have also been shown to consume the fruits and transport the seeds. The phenomenon has been identified in many Juniperus species; Adams and Thornburg (2010) provide a recent review.
Axelrod, D.I. 1975. Evolution and biogeography of Madrean-Tethyan sclerophyll vegetation. Annals of the Missouri Botanical Garden 62:280–334.
This page co-edited with M.P. Frankis, 1999.03.
Adams, Robert P. 1969. Chemosystematic and numerical studies in natural populations of Juniperus. Ph.D. dissertation, University of Texas.
Adams, Robert P. 1993. Juniperus. Flora of North America Editorial Committee (eds.): Flora of North America North of Mexico, Vol. 2. Oxford University Press. This document is available online. Go to http://www.efloras.org, click on "Flora of North America," and search for "Juniperus."
Adams, Robert P. 2008. Junipers of the World: The Genus Juniperus. Second edition. Trafford Publishing. Brief versions of the descriptions are available online at Adam's website, www.juniperus.org.
Adams, R. P. and D. Thornburg. 2010. Seed dispersal in Juniperus: A review. Phytologia 92(3):424-434. Available at www.phytologia.org.
Adams, R. P. and T. A. Zanoni. 1979. The distribution, synonymy, and taxonomy of three junipers of the southwest United States and northern Mexico. Southwest Naturalist 24:323-330.
Adams, R. P., E. von Rudloff and L. Hogge. 1983. Chemosystematic studies of the western North American junipers based on their volatile oils. Biochem. Syst. & Ecology 11:85-89.
Farjon (2005) provides a detailed account, with keys and a cladistic tree.
Hall, M. T. 1952. Variation and hybridization in Juniperus. Annals of the Missouri Botanical Garden 39:1-64.
Last Modified 2017-12-29