James D. Mauseth

"Not all s evolve at the same rate, some early species were actually so well adapted that they competed successfully against newer species. are so well suited to life in oceans, lakes, and streams that they still thrive even though most features present in modern, living algae must be more or less identical to those present in the ancestral algae that lived more than 1 billion years ago. Features that seem relatively unchanged are relictual features (technically known as , formerly called primitive features). Like the algae, s are well-adapted to certain habitats and have not changed much in 250 million years; they too have many relictual features. Modern conifers are similar to early ones that arose around 320 millions years ago. The most recently evolved group consists of the flowering plants, which originated about 100 to 120 million years ago with the evolution of several features: flowers, broad, flat, simple leaves, and that conducts water with little friction. The members of the (sunflowers, daisies, and s) ... have many features that evolved recently from features present in ancestral flowering plants. These are derived features (technically known as , formerly called advanced features (i.e., they have been derived evolutionarily from ancient features). One recent (highly derived ) feature in the asters is a . The terms "primitive" and "advanced" are avoided in that they imply inferior and superior."

"Ancestral presumably had abundant, fibrous, heavily , similar to that present in the relictual, leaf-bearing genus '. During the evolutionary radiation of the subfamily , diverse types of bodies and woods arose. Several evolutionary lines have retained an abundant, fibrous wood: all wood cells, even ray cells, have thick lignified walls, and axial is only scanty paratracheal. Aside from a diversity of vessel diameters, there seems to be little protection against during water-stress, and little capacity. This strong wood permits the plants to be tall and to compete for light in their tree-shaded semi-arid habitats. In other evolutionary lines, the wood lacks fibres, and almost all cells have thin, unlignified walls. Vessels occur in an extensive matrix of water-storing parenchyma, and tracheids are also abundant, constituting over half the axial tissue in some species. There is excellent protection against cavitation, but little mechanical support for the plant body; however, these plants are short and occur in extremely arid, unshaded sites. Scandent, vinelike plants of two genera produce a dimorphic wood—while their shoots are extending without external support, they produce fibrous, lignified wood, but after leaning against a host branch, they produce a parenchymatous, unlignified wood."

"s are technically known as angiosperms. Flowers are reproductive structures, some parts produce , which carry sperm cells, other parts have egg cells. During reproduction, new embryos form as part of a seed, and all seeds occur inside fruits. Plants with obvious flowers, such as roses, s, s, and lilies are flowering plants ... But in many other angiosperms, the flowers are tiny and inconspicuous, for example, the flowers of grasses are so small and pale you might never notice them, and the same is true for those of s, s, , and ... Other angiosperms have large, obvious flowers, but they bloom so rarely—at least in cultivation—that many people mistakenly assume that they never flower. are a good example of this: when kept on a , potted cacti may survive and grow without being healthy enough to flower, but in nature they produce spectacular flowers that no one could miss. All angiosperms have s, that is, tissues that conduct water and nutrients from one part of the plant to another."