Flowers of Grass

 

Orchard grass flowers

Orchard grass flowers

What is even more numerous than the “leaves of grass”? In most cases, the flowers of grass. Anyone who has let their lawn go unmowed for several weeks will begin to see the flowers of the various species of grass. They are not spectacularly colored, but their geometry is often delicately pretty and close inspection reveals a structure that is unique to this family and represents a different and relatively recent evolutionary path.

Grasses were recognized as a distinct family early on in the history of the classification of living things. Their older name, Graminae, dates back to at least Carolus Linnaeus. In most systematics texts the grasses are called the Poaceae. It is one of the eight old family names that were retained when the International Botanic Congress decided (the “St. Louis Code) in 1999 to make all family names end in -aceae (while the root was derived from a characteristic genus name within the family). Consequently, you see references to the Poaceae (Graminae) or simply to the Graminae by “old school” systematists. Other examples include the Fabaceae (Leguminosae; bean family) and the Apiaceae (Umbelliferae; carrot family).

Before the era of DNA analysis plants were often classified, at least in part, based on their flower morphology. The distinctness of the grass flower components must have helped botanists identify them as a coherent group fairly early on.

Parts of a grass flower

Parts of a grass flower

There are no petals or sepals in a grass flower. Instead the female (style and stigmas) and male (filament and anthers) are bracketed by a palea and a lemma, which are derived from scales (not leaves). This combination is called a floret.

Several florets are arrayed with varying geometry along a rachilla. At the base of this collection of florets are an upper and a lower glume. Collectively these components are referred to as a spikelet.

If the spikelets are borne directly attached to a central stalk, then the whole array is called a spike. When lateral stalks project bearing spikelets, the flower is a raceme. If those stalks bear projecting stalks, then it is a panicle. These are called forms of inflorescence.

Some genera, like Sisyrichium or the blue-eyed grasses, are not true grasses. They have long, thin leaves with parallel veins, but their flowers consist of petals and sepals. They are most closely related to irises.

Amber waves of grain

Amber waves of grain

Grass flowers are almost always green. They don’t need color to attract pollinators, because they are anemophilous; their pollen is distributed by the wind. After they are finished pollination and begin seed formation, the spikelets tend to turn brown or golden. The “amber waves of grain” in “America the Beautiful” reference this phenomenon. A great many “cereal grains” are grasses, including wheat, barley, rice, sorghum, millet, rye, oats, and triticale (a hybrid of wheat and rye). Quinoa and buckwheat are examples of non-Poaceae cereal grains.

Corn is an exception within the Poaceae family in that it bears separate male and female flowers; most grass flowers are hermaphroditic, that is, bear both male and female organs. In corn the male flowers are borne at the tops of the plants and the female flowers are carried at the nodes where the leaves emerge. Once fertilized they turn into ears of corn. In British English “corn” actually refers to any cereal grain with “maize” being the name given to what we call “corn.”

Ornamental grasses, which are increasingly popular in landscaping, have more showy flowers than lawn or cereal grasses. Cortaderia selloana or Pampas grass is perhaps the most well known of the ornamental grasses. It can grow over ten feet tall and the flowers taking the form of feathery plumes nearly a foot in height. The genus Miscanthus (of the tribe Andropogoneae) has several species of varying sizes that bear plumes that are wispier than those of Cortaderia. In addition to being used as ornamentals, some hybrid species are being used as biofuels because of their spectacular rate of growth.

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