By Caleb Hute, Consulting Botanist
Figure 1. Purple needlegrass (Stipa pulchra), the State Grass of California, nods in the wind in the Bowman Canyon serpentine grassland on in the Mount Burdell Preserve.
Spring has sprung, and even as the recent heat wave turns hillsides brown, wildflowers are blooming all across the county. The gorgeous wildflower displays we are lucky enough to receive fit nicely with the green background which accompanies them. Today I want to talk about the background that occurs between and around the flowers that you usually ignore: grasses.
Evolutionary Significance
You might not believe it, but grasses are actually part of the larger evolutionary clade of plants referred to as angiosperms, or flowering plants. This family is immensely successful with grasslands, which are assemblages of plants where grasses are most prevalent, being found on every continent except Antarctica. One secret of success of some grass species is C4 photosynthesis, an adaptation which allows plants to operate their photosynthetic systems more efficiently in warm climates (ex. corn). Another adaptive advantage is a lack of reliance on pollinators; grass species are wind pollinated. This is why grasses don’t appear as showy as other flowering plants – they have no need to draw in pollinators with elaborate floral displays, and over evolutionary time, have lost most of the bright colors and typical attractive morphologies we associate with spring wildflowers.
Usefulness for Humans
However, despite lacking conventional beauty, grasses still dominate human existence. Much of the world’s calories come from different species of grass, including rice, corn, oats, wheat, and barley. Bamboo, while not native to the United States, has been used as a building material within its native range for centuries. Lawns, which have become ubiquitous aspects of suburban America, rely on another of the many adaptations of grass – the ability to be cut back, and continue living and growing. This adaptation is the result of a complex evolutionary relationship with grazing herbivores. It is unsurprising then, that many grass species grow even more robustly after being nibbled. The mechanism which allows this are special growing points that allow continued growth from the middle of the leaf, even if the tip has been removed.
Flower Characteristics
Although they may seem so different, certain characters of a flower may still be recognized in grass species. Being able to recognize these characters is perhaps fun (or possibly frustrating) for the casual plant lover, and essential for botanists who are seeking to identify plants all the way to a species or subspecies level. Firstly, we must talk about the structure of an inflorescence, or the complete flowering structure of a plant (See figure 2 below). While some plants may only have one flower per inflorescence, plants in the grass family typically have more than one. These highly modified and reduced flowers are grouped into units referred to as spikelets, which are small bundles of highly modified flowers subtended by a set of modified leaves (bracts) called glumes.
Figure 2. Grass morphology as found in common, non-native grass slender wild oats (Avena barbata). An ovary, once pollinated, develops into a fruit.
Spikelets are usually attached to a single central axis without a stalk (referred to as being ‘sessile’) or attached to the axis by a branch. Each branch will have one or more spikelets. Each individual modified flower within a spikelet is referred to as a floret. Each of these florets is wrapped in two specialized bracts called the lemma and palea. At the very center of a (bisexual or pistillate) floret, you will find the giveaway of a modified flower – an ovary which develops into a fruit (botanically, not culinarily speaking). In the case of grasses, the fruit produced forms a hard, indehiscent shell around the embryo, and is referred to as a caryopsis or grain. The energy dense embryo of this fruit is what supplies the world with all the great grass derived food we rely on, from simple foods like oatmeal, to food products like corn syrup, which are found in innumerable products all across the globe.