By Caleb Hute, Consulting Botanist
Serpentine reed grass (Calamagrostis ophitidis) at Ring Mountain Preserve by Caleb Hute
As summer closes in, you might notice the hillsides are undergoing a transformation from green to brown. This change is driven mainly by the senescence of the non-native annual grasses which dominate California grasslands. In some settings, these grasses may comprise as much as 99% of all plant biomass. A few months ago, I discussed the general terminology used by botanists to describe the parts of grass inflorescences and flowers (you can find that article here). While we still have some grasses left to examine, I want to dive into some other vegetative characteristics which are used for grass species identification.
The first distinction which may be useful to know what is considered annual or perennial. Annual grasses complete their entire life cycle in one year, from germination to producing seed. Perennial grasses live more than one year but often die back annually. Perennial grasses have a basal ‘crown;’ effectively a cluster of buds near the soil surface, from which new stems sprout each season. Many of California’s most iconic native grass species are perennial, such as wild ryes (Elymus spp.) and fescues (Festuca spp.)
Each stalk which rises from the crown (referred to as a tiller) consists of nodes, which are the solid, swollen sections of stem from which leaves emerge, and areas between the nodes, commonly referred to as internodes, which are hollow. Nodes harbor meristematic tissue (undifferentiated tissue, comparable to human stem cells), which produce new leaf and stem growth. Each new leaf that emerges usually consists of three main parts; a sheath which wraps around the stem, a blade, which is flat or variously folded but does not wrap around the stem, and a collar region, located between the two.
The collar region is an especially morphologically complex portion of a grass. The main part of this region is the collar – a band of meristematic tissue, which wraps around the stem between the blade and sheath, and allows the leaf blade to continue growing outward even if the tip has been broken off. The collar often is a different color than the rest of the leaf. At the “front” of the collar region, where the leaf sheath overlaps or closes, small claw or ribbon-like projections off of the collar may be present, called auricles. More often than not, auricles match the collar in texture and color, though they may be modified in different ways, including being hairy or wrinkled. Towards the back of the collar region, most grasses have a small flap of tissue called a ligule. This tissue varies in its qualities, but most frequently is membranous, fragile and readily shredding in age.
The name Ligule comes from the Latin word for strap, which is a modification of the Latin word for tongue. To help me remember the name of this feature, I like to think about a leaf sheath without the stem, with the ligule at the opening of the sheath, which resembles a mouth with a tongue hanging out.
Real examples of stem and collar region components (various species)
Some perennial grasses form dense clumping colonies. Such grasses are referred to as cespitose. One way which grasses achieve this look is through short creeping aboveground stems, called stolons, or subterranean stems called rhizomes. However, grasses without such structures may also exhibit this habit, such as the tightly clustered native California fescue, Festuca californica, which forms large, soft looking mounds on the back slopes of Mount Burdell.
Cespitose Festuca californica on Mount Burdell in Olompali State Park by Caleb Hute
Each tiller may be topped by an inflorescence, depending on the developmental stage of the stalk, what level of stress the plant is under, and seasonal timing. An inflorescence is the complete flowering structure of a plant, and in grasses is made up of smaller units called spikelets. Most importantly, the inflorescence contains flowers, which produce seeds, which allow grasses to proliferate.
There are endless variations to structures on grasses across species. Some species add hair, some add color, others have lost certain structures entirely. While some of these modifications are subtle, understanding the basic structure of grass should give you a solid basis for understanding species with unique and novel characteristics.
