Brome Grasses, belonging to the genus Bromus, represent a large group of approximately 160 species found across the globe in temperate regions. This genus includes grasses valued for forage and erosion control, as well as several that are considered problematic weeds. Understanding the visual characteristics of Brome Grass is the first step in distinguishing between these beneficial and invasive varieties.
Overall Structure and Foliage
Brome grasses are cool-season plants that typically grow between 12 to 40 inches tall, forming either dense clumps or wide-spreading sods depending on the species. A defining feature of the Bromus genus is the structure of the leaf sheath, which is fused into a closed tube around the stem for a significant portion of its length. This closed sheath often gives the base of the leaf a distinctive, almost “V-neck” appearance where it meets the stem.
The texture and presence of hairiness on the leaves and sheaths is a major visual differentiator among species. Some varieties, like Smooth Brome (Bromus inermis), have stems and leaves that are largely hairless. Others, such as Downy Brome (Bromus tectorum), are characterized by a dense covering of soft, downy hairs. At the junction of the leaf blade and the sheath, all Brome grasses possess a membranous ligule. Furthermore, the leaf blade of Smooth Brome often displays a noticeable “M” or “W”-shaped crimp or watermark located about one-third of the way down from the tip.
The Distinctive Seed Heads
The reproductive structure, or inflorescence, of Brome Grass is a loose, branching cluster known as a panicle, which usually forms in late spring or early summer. The overall shape of this panicle provides an immediate clue for identification, as it can range from a dense, erect cluster to a delicate, open structure that gracefully nods or droops. This variation is important: a semi-compact, upright panicle suggests one species, while a loose, decidedly nodding head points to another.
Within the panicle, the flowers are grouped into small units called spikelets. Each spikelet is typically large and robust, containing multiple individual flowers. The length and form of the awns, which are the stiff, bristle-like projections extending from the spikelet’s outer covering (the lemma), are the most telling feature. Many Brome species are heavily awned, with some awns reaching over an inch long, giving the seed head a shaggy or bristled appearance. Conversely, a few species, such as Smooth Brome, are awnless or feature only extremely short, barely visible awns.
Identifying Common Brome Species
Applying these features allows for the differentiation of the most common Brome species, which generally fall into two categories: perennial forage grasses and weedy annual grasses.
Smooth Brome
Smooth Brome (Bromus inermis) is a perennial forage grass identified by its hairless leaves with the “M”-shaped watermark and its awnless, semi-compact panicle. The plant spreads aggressively through underground stems called rhizomes, forming a dense sod.
Downy Brome
Downy Brome (Bromus tectorum), also known as Cheatgrass, is a problematic winter annual weed. It lacks rhizomes and grows in tufts, distinguished by its densely soft, hairy leaves and sheaths. Its seed head is an open, distinctly nodding panicle with long, slender awns that are often purple-tinged at maturity.
Rescue Brome
Rescue Brome (Bromus catharticus) is another annual type. It is loosely tufted with lightly hairy leaves and a loose, nodding panicle. Its spikelets are strongly compressed and usually have only very short awns.