Podocarp family, [Chinese].
In this treatment, 173 species in 18 genera:
It has been treated as an order: Podocarpales Pulle ex Reveal 1992, and many of its constituent genera, including Nageia, Phyllocladus and Saxegothaea, have been raised to the rank of Family by previous authors. Phyllocladus was traditionally thought to be the most atypical genus in the family, and it was often treated as Phyllocladaceae Bessey 1907; but molecular analyses (described below) have repeatedly shown Phyllocladus to be firmly rooted within one of the major clades of the Podocarpaceae.
The cladogram shown at left summarizes Podocarpaceae phylogeny as hypothesized by Biffin et al. (2011). Yellow lines show the principal clades; blue lines the inferred phylogeny on the basis of morphological, molecular and other (climate) characters; red lines the outgroup Araucariaceae; and green lines are error bars for each node (the 95% highest probability density divergence times). The time scale shows estimated times of divergence using Bayesian-relaxed clock analysis of plastid DNA. The analysis supports the monophyly of Podocarpus genera. The timeline is consistent with the fossil record, especially in showing a divergence between Araucariaceae and Podocarpaceae about 205 million years ago, and in the times of appearance of major genera.
The analysis of Biffin et al. (2011) can be compared to that of Knopf et al. (2011), performed at about the same time and with a comparable level of detail. Knopf et al. produce several cladograms based on types of molecular data, as well as a consensus tree based on combined analysis of molecular and morphological data. These cladograms reveal uncertainties about the structure of the major clade that includes Prumnopitys, the placement of Saxegothaea, and the relationship between Microcachrys and Phaerospharea, but overall show remarkable consistency with the analysis of Biffin et al. with regard to relationships of genera within the family. Also, both Knopf et al. and Biffin et al. confirm in their analyses that the strongest morphological indicators of phylogenetic relationships within the Podocarpaceae are characters of leaf anatomy.
Many of the genera described here were originally lumped into the huge catchall genus Podocarpus or the also-very-large genus Dacrydium, and appear as such in much of the literature. Here is a brief and simplified chronology of how the podocarps have been subdivided at the generic rank:
|1786 - Solander||Dacrydium described.|
|1788 - Gaertner||Nageia described, begins a long and complex history (mostly 1840 to 1990) with the net result of species being moved from Podocarpus into Nageia.|
|1807 - L'Heritier||Podocarpus described, begins accumulating species, a process that continues today.|
|1825 - Richard||Phyllocladus described. No one ever confuses with it any of the other podocarps.|
|1845 - Hooker f.||Microcachrys described.|
|1850 - Archer||Pherosphaera described, lumping several new species with Microcachrys.|
|1851 - Lindley||Saxegothaea described.|
|1861 - Phil.||Prumnopitys described but is monotypic for 117 years.|
|1903 - Pilger||Acmopyle described.|
|1969 - de Laubenfels||Nageia species reassigned to the new genus Decussocarpus
Dacrycarpus segregated from Podocarpus
Falcatifolium described, mostly with new species.
|1972 - de Laubenfels||Parasitaxus described.|
|1978 - de Laubenfels||Seven Podocarpus species assigned to Prumnopitys.|
|1982 - Quinn||Halocarpus, Lagarostrobos, and Lepidothamnus segregated from Dacrydium.|
|1987 - de Laubenfels||Decussocarpus invalidated and its species reassigned to Nageia.|
|1989 - Page|| Afrocarpus segregated from Nageia and Podocarpus
Retrophyllum segregated from Nageia.
|1995 - Molloy||Manoao segregated from Lagarostrobos.|
|2004 - Brummitt et al.||Sort out the extremely confused nomenclature of Diselma, Microcachrys, Microstrobos, and Pherosphaera, designating a number of new types.|
Evergreen shrubs or trees, usually with straight trunk and more or less horizontal branches. Leaves usually spirally arranged, sometimes opposite, scale-like, needle-like, or more apart, flat and leaf-like, linear to lanceolate. Monoecious or dioecious. Pollen cones usually catkin-like; stamens numerous, close together, imbricate, each with 2 sporangia; pollen grains usually winged. Female cones maturing in one year, much reduced to a few fleshy bracts or scales, pendant, usually borne on a thin peduncle, containing a single inverted ovule. Seeds completely covered by a fleshy structure referred to as an epimatium, wingless. Epimatium and integument sometimes connate and forming a leathery testa. Cotyledons 2, with 2 parallel vascular bundles (Van Royen 1979, Silba 1986).
All investigated Podocarpaeceae have vesicular-arbuscular mycorrhizas (Newman and Reddell 1987, Brundrett 2008 and citations therein).
The family is predominantly found in the Australasian region, with most taxa native from New Zealand to SE Asia. Most of species are not of wide distribution, being confined to one or a few islands, viz. Tasmania, New Zealand, New Caledonia, New Guinea, Philippines, Borneo. Some species of the genera Dacrydium, Lepidothamnus, Nageia, Podocarpus, Prumnopitys and Saxegothaea are found beyond Australasia, in India, Japan, China, Africa, the Caribbean and the New World south from Mexico to Chile. Of these, Saxegothaea, a monotypic genus found in Chile and Argentina, is the only genus with no representatives in the Australasian region. Most members of the family are trees native to wet tropical or subtropical (often, tropical mountains) forests. A few are small trees or shrubs native to forest understory environments.
Biffin et al. (2011) provide a thoughtful exploration of the relationship between conifers and angiosperms that is focused on Podocarpaceae, one of the few conifer groups that has continued to speciate and thrive within an angiosperm-dominated biome, specifically, the wet tropical forest. They find that, like most other conifer families, the Podocarpaceae originally had scale-like or needle-like foliage, but that adaptive radiation (genera Acmopyle through Podocarpus in the cladogram at left) during the past 65 million years has been characterized by the emergence of various types of flattened, often broad leaves, which now characterize most species in the family. This adaptation, which facilitates efficient light harvesting in shaded environments, has emerged during the time when the podocarps have been in direct competition with angiosperms, and likely explains why the podocarps have continued to prosper in wet tropical forests while most other conifers are excluded from the biome; the timing of this change also coincides with to larger ecological and climatic changes that have been linked to evolution of tropical broadleaf habit in the angiosperms. It also appears that foliage flattening has evolved independently at least five times in the family. Although Biffin et al. don't mention it, the other gymnosperm genera found in the wet tropics, Agathis and Gnetum, have also developed flattened, broad leaves.
Quite possibly the rimu, Dacryium cupressinum, but there are several other species, possibly equally old or older, that have not been well studied.
Although the second-largest conifer family, the Podocarpaceae are far less well-known than the other two big families, Pinaceae and Cupressaceae. There are several possible reasons for this situation. The Podocarpaceae are chiefly a tropical family, thus few species have attracted interest among the European horticultural community and few species are known for their ornamental value. With few and local exceptions (e.g., New Zealand), the family does not otherwise possess great economic importance. Only a few species are exploited for timber, and those are for the most part greatly diminished by overcutting. Most species in the family are found in tropical forests that are dominated by a great many species of angiosperm trees, so the family does not possess the ecological significance attached to the Pinaceae or Cupressaceae. Finally, the family is primarily found in Third World countries, where plants in general receive little research unless they be economically important. This is a regrettable state of affairs, because the Podocarpaceae probably contain more species threatened by overcutting and habitat loss than any other family. In view of the above considerations, in seems inevitable that many taxa described here are bound for extinction in the coming decades.
See the generic and species descriptions.
Netta E. Gray did much of the early work on Podocarpus and its segregates (Afrocarpus, Nageia, Prumnopitys, and Retrophyllum). She was accordingly honored by D.J. de Laubenfels with Podocarpus grayae de Laub. 1985. The September 1973 Plant Science Bulletin carried this brief biography of Mrs. Gray:
Netta E. Gray worked and studied with John T. Buchholz at the University of Illinois, completing her Masters degree in Botany. She was particularly interested in the genus Podocarpus. The work she started with Buchholz and later carried on herself was a careful systematic treatment of each of the sections of Podocarpus. She was concerned with the systematic importance of anatomical details, and the geographical distribution and evolution of the genus. As a result of her diligent study of the group she became one of the world's authorities on this genus and had such visitors as R. Florin come to her door. She lived with her husband Professor Stephen W. Gray near Atlanta, Georgia and taught at Agnes Scott College in Decatur, Georgia. She continued an active interest in research and publication about the genus, Podocarpus, as well as the Gymnosperms as a whole, until her death on August 24, 1970.
Brundrett, Mark. 2008. Mycorrhizal Associations: The Web Resource. mycorrhizas.info, accessed 2009.06.09.
Newman, E.I. and P. Reddell. 1987. The distribution of mycorrhizas among families of vascular plants. New Phytologist 106: 745-751.
Barker, N.P., E.M. Muller, and R.R. Mill. 2004. A yellowwood by any other name: molecular systematics and the taxonomy of Podocarpus and the Podocarpaceae in southern Africa. South African Journal of Science 100:629-632.
Buchholz, J.T. and N.E. Gray. 1947. A Fijian Armopyle. Journal of the Arnold Arboretum 28: 141-143.
Buchholz, J. T. and N. E. Gray, 1957. Contributions to the Flora of Venezuela - IV. Podocarpaceae. Fieldiana Botany 28: 759-772.
Conran, J.G., G.M. Woods, P.G. Martin, J.M. Dowd, C.J. Quinn, P.A. Gadek and R.A. Price. 2000. Generic relationships within and between the gymnosperm families Podocarpaceae and Phyllocladaceae based on an analysis of the chloroplast gene rbcL. Australian Journal of Botany 48:715–724.
Gray, N.E. and J.T. Buchholz. 1948. A Taxonomic Revision of Podocarpus. III. The American Species of Podocarpus: Section Polypodiopsis. Journal of the Arnold Arboretum 29: 117-122.
Gray, N.E. and J.T. Buchholz. 1951. A Taxonomic Revision of Podocarpus. V. The South Pacific Species of Podocarpus: Section Stachycarpus. VI. The South Pacific Species of Podocarpus: Section Sundacarpus. Journal of the Arnold Arboretum Vol. 32: 82-92.
Gray, N.E. 1953. A Taxonomic Revision of Podocarpus. VII. The African Species of Podocarpus: Section Afrocarpus. Journal of the Arnold Arboretum 34: 67-76.
Gray, N.E. 1953. A Taxonomic Revision of Podocarpus. VIII. The African Species of Section Eupodocarpus, Subsections A and E. Journal of the Arnold Arboretum 34: 163-175.
Gray, N.E. 1955. A Taxonomic Revision of Podocarpus. IX. The South Pacific Species of Section Eupodocarpus, Subsection F. Journal of the Arnold Arboretum 36: 199-206.
Gray, N.E. 1960. A Taxonomic Revision of Podocarpus. XII. Section Microcarpus. Journal of the Arnold Arboretum 41: 36-39.
Gray, N.E. 1962. A Taxonomic Revision of Podocarpus. XIII. Section Polypodiopsis in the South Pacific. Journal of the Arnold Arboretum 43: 67-79.
Gray, N.E. 1969. An Interpretation of Podocarpus in Time and Space. The Bulletin of Georgia Academy of Science 27: 144-147.
Hill, R.S. and T.J. Brodribb. 1999. Southern conifers in time and space. Aust. J. Bot. 47:639–696.
The authors provide an earlier version of the "flattened foliage in the wet tropics" hypothesis.
Kelch, D.G. 1998. Phylogeny of Podocarpaceae: comparison of evidence from morphology and 18S rDNA. American Journal of Botany 85(7):986–996.
Turner, B.J. and L.A. Cernusak (eds.). 2011. Ecology of the podocarpaceae in tropical forests. Washington, DC: Smithsonian Institution Scholarly Press. vii+207.
Last Modified 2014-03-29