5.3 Class Magnoliopsida – flowering plants - Cambridge University ...

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240 ORDERING THE PATHS OF DIVERSITY Figure 5.91. Geraniales: Geranium. Rosids and Asterids The remaining eudicots form two great lineages, the crassinucellate (thick nucellus) Rosids and the tenuinucellate Asterids, each split into two sister lineages (Eurosid 1 and 2, Asterid 1 and 2). The tenuinucellate condition is a derived feature of the ovule where the tissue layer, the nucellus, surrounding the developing megasporangium/embryosac is thin. There are various kinds of crassinucellate condition. Each main and sub-lineage is very variable but exhibits particular evolutionary tendencies. For example, all the nitrogenfixing families are found in the Eurosid I group: Casuarinaceae, Myricaceae (Fagales), Eleagnaceae, Rhamnaceae, Ulmaceae (Rosales), Fabaceae (Fabales) and Coriariaceae (Cucurbitales). There are well defined families like the Fabaceae, almost stereotypical with its characteristic fruit, the legume, and characteristic forms of flowers and inflorescence, or large and diverse families, like the Rosaceae, that have proved evolutionarily flexible. 5.3.7 Rosids Rosid orders or even families are very diverse in their floral structure. Most of the ecologically (and economically) important trees from forests and savannas around the world are Rosids. They include the tallest flowering plants such as the eucalypts, the mahoganies in the tropics, the savanna acacias, and oaks, maples and beech from temperate forests. Percentage of families Rosids Asterids stipules 66% with 16% with stamens 58% with two whorls 79% single whorl corolla 97% free 75% fused integument(s) 94% two 87% one nucellus 92% crassinucellate 91% tenuinucellate endosperm 96% nuclear 75% cellular iridoids 5% present 61% present Basal Rosids geraniales (geraniums) The Geraniales include one large family, the Geraniaceae, and several very small ones. One interesting feature they share is the presence of glands on the margin of the leaf. They have pentamerous obdiplostemonous flowers with a persistent calyx. The two largest genera Pelargonium and Geranium produce similar beaked fruits but differ in the former having monosymmetric flowers and a nectariferous pedicel (Figure 5.91). The Geraniaceae are commonly herbs with jointed stems but the other families in the order include shrubs and trees.
crossosomatales These are a small order of shrubs and small trees adapted to dry habitats. myrtales (eucalypts and myrtles) The Myrtales have an uncertain relationship to either main Eurosid clade. Many have flowers with a large number of stamens (Figure 5.92). However, not all show this pattern. In the Melastomataceae (4750 species) the stamens are dimorphic with showy colourful outer stamens and short pollen-producing inner ones. The Onagraceae (650 species) have only four or two stamens and a long hypanthium tube. These families are significant as herbs or shrubs but the Myrtales includes the Myrtaceae and Combretaceae, which are highly significant as trees in the tropics especially in semi-arid areas of Australia (Eucalyptus ∼450 species) and Africa (Combretum ∼250 species, and Terminalia ∼150 species). Eurosid I zygophyllales (creosote-bush and lignum-vitae) There are several species important in arid and saline soils like Larrea, Balanites (thorny) and Zygophyllum. Larrea divaricata, the Creosote bush of the deserts of USA and Mexico is strongly allelopathic. celastrales (spindle-tree and ebony) A member of the Celastraceae familiar to us is the widely planted garden plant Euonymus, the spindle-tree, with its characteristically angled fruit. Maytenus (ebony) is an important tree in warmer areas throughout the world. The flowers generally have a broad disk with the ovary submerged in it. malpighiales (spurges, violets, willows and passion-flowers) The diversity of the order is illustrated by a comparison of the families Violaceae (pansies), Passifloraceae (passion flowers), Linaceae (flax), Salicaceae (willows) and Clusiaceae (Hypericum), each with a very different kind of flower. Perhaps its most interesting family is the latexproducing Euphorbiaceae that includes such important genera as Ricinus, Euphorbia, Manihot and Hevea (rubber) (see Figure 5.94). oxalidales (bermuda buttercup and wood sorrel) The order includes trees, shrubs, lianes and herbs (Oxalis) and also the insectivore Cephalotus (Cephalotaceae). (a) (b) (c) (d) 5.3 CLASS MAGNOLIOPSIDA – FLOWERING PLANTS 241 Figure 5.92. Myrtales: Eucalyptus. (a) (b) Figure 5.93. (a) Viola; (b) Linum. Figure 5.94. Euphorbiaceae: the inflorescence (a cyathium) mimics a flower: (a) succulent euphorb with a crown of leaves and cyathia; (b) a cyathium showing the arrangement of a central female floret surrounded by male florets and an involucre of bracts; (c) a single female floret; (d) a single male floret.
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Page 15 and 16: Basal Eudicots Basal eudicots such
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Page 21 and 22: (all Faboideae/Popilionoideae). All
Page 23 and 24: tri-foliolate leaves. Many of these
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Page 27 and 28: apiales (umbels and ivy) There are
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