Families Poaceae and Liliaceae (Monocots)

Poaceae (the grass family) and Liliaceae are the two monocotyledonous families included in this chapter's syllabus, and while both share the basic features common to all monocots -- a fibrous, adventitious root system, leaves with parallel venation, and floral parts typically arranged in multiples of three -- their floral structures diverge sharply once examined closely, largely because the two families rely on entirely different pollination strategies.

Poaceae: vegetative characters. The grass stem, called a culm, is cylindrical and distinctly jointed: it is generally hollow through each internode but solid at every node. Leaves have a long sheath that wraps around the culm, a narrow blade, and, at the point where sheath meets blade, a small membranous (or sometimes hairy) outgrowth called the ligule, which helps keep water and small pests from entering the sheath.

Poaceae: floral characters. Because grasses are wind-pollinated, their individual flowers are highly reduced in size and structure, and are grouped together into small compact units called spikelets, which are in turn arranged into larger inflorescences. Within each floret, the true perianth is reduced to just two minute, scale-like structures called lodicules, whose swelling at the time of flowering helps force the floret open. The androecium usually has three stamens, each with a long, flexible (versatile) filament and an anther that dangles well outside the floret -- an arrangement well suited to releasing large amounts of pollen into moving air. The gynoecium has a superior ovary formed of two or three fused carpels, unilocular with a single ovule, and topped by one or two feathery, much-branched stigmas that efficiently trap airborne pollen grains -- again, a structure clearly adapted to wind pollination rather than to attracting an animal pollinator.

Poaceae: fruit. The fruit is a caryopsis, distinguished by the fact that its thin seed coat is fused tightly and inseparably to the surrounding fruit wall -- this is the familiar grain of wheat, rice or maize, which is technically a one-seeded fruit, not simply a seed.

Liliaceae: floral characters. Liliaceae, by contrast, retains the large, showy, insect-pollinated flower typical of many ornamental monocots. Its perianth is not divided into a separate calyx and corolla; instead, all six members look alike and are petal-like (petaloid), described together as P3+3 (two whorls of three), often brightly coloured and sometimes fused at their base into a short tube. The androecium has six stamens, again arranged in two whorls of three, matching the six perianth members. The gynoecium is formed of three fused carpels (G(3)), giving a superior, trilocular ovary with axile placentation and numerous ovules in each chamber.

Liliaceae: fruit. The fruit is typically a capsule that splits open at maturity, though some genera, such as Asparagus, instead produce a fleshy berry. …