Dipsacales eurosids I
Figure 2-5. Ordinal classification of angiosperms, adapted from the Angiosperm Phylogeny Group (1998). Resin-producing orders are in boxes with solid borders; those described as resin producing, but unsupported by adequate chemical data, are in boxes with dashed borders. Also see Appendix 2.
lies has been suggested, at one time or another, as the most primitive extant angiosperm. Because of incomplete knowledge of the phylogenetic relationships of angiosperms, the early divergent clades continue to be analyzed and discussed. This group is referred to as the basal group or the nonmonocot paleoherbs. APG did not name monocots and eudicots formally because it could not be determined at which rank these two taxa should be recognized (Figure 2-5). Nor were commelinoids (monocots) or rosids and asterids (core eudicot subgroups) formally named. These groups, however, are commonly known as the subclasses Commelinidae, Rosidae, and Asteridae, respectively, and I occasionally refer to them in this manner. Within the eudicots, there is increasing support for the large subgroup, the core eudicots, which in turn is divided into rosids and asterids, each of which is increasingly considered monophyletic. There is further division into eurosids I and II and euasterids I and II, with one rosid and two asterid orders placed outside these groups (Figure 2-5). Some families are recognized as belonging to one of the major groups but their ordinal position remains uncertain.
Resin production is scattered throughout the flowering plants, which is generally true for the various kinds of secondary chemicals. The distribution of resin-producing plants among the 40 orders recognized by APG is shown in Figure 2-5. This dispersion is even clearer in the listing of genera within families (Appendix 2).
Resins are produced primarily by woody angiosperms, that is, flowering trees and shrubs, but they also occur in a few herbs. The most copious quantities are produced in the trunks of trees, particularly those in subtropical and tropical climates (Langenheim 1969, 1990). However, the greatest amount of resin produced by organ weight may be that coating leaves of shrubs in semiarid regions (Dell and McComb 1978). Not all resins of species within a genus listed in Appendix 2 have been reported as used by humans or as playing an ecological role in the plant. Only species for which the significance of resin to plants or humans has been recorded in the literature are discussed in the following chapters.
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