Understanding the intricate details of grass species botanical descriptions is fundamental for students of botany, agriculture, and ecology. This article provides a comprehensive overview of several important grass genera and their distinct species, helping you differentiate them based on their unique morphological characteristics.

Exploring Grass Species Botanical Descriptions

Grasses, members of the Poaceae family, exhibit a remarkable diversity in their structure, from their roots and stems to their intricate floral parts. Delving into the specific attributes of each species allows for accurate identification and a deeper appreciation of their ecological roles.

Genus Bromus: A Detailed Look

The genus Bromus includes various brome grasses, each with defining characteristics in their fertile spikelets, glumes, and florets.

1. Bromus carinatus (California Brome)

Habit: A short-lived perennial, with culms typically 30–100 cm long. Its leaf sheaths are tubular, closed for about 75% of their length, and pilose.
Inflorescence: An open, lanceolate panicle, 10–25 cm long. Primary branches are appressed or ascending.
Fertile Spikelets: Elliptic, strongly laterally compressed, 15–45 mm long, comprising 4–12 fertile florets. They disarticulate below each fertile floret at maturity.
Glumes: Persistent and dissimilar. The lower glume is lanceolate (5–9 mm long, 3-veined), and the upper glume is lanceolate (10–15 mm long, 5–7-veined), both with an acuminate apex.
Florets: Fertile lemma is ovate (11–15 mm long), herbaceous, keeled, and 7-veined. Its surface is smooth or scaberulous, glabrous to pubescent, with a dentate, 2-fid, acute, awned apex (awn 3–15 mm long). The fruit is a caryopsis with an adherent, hairy, fleshy apex.

2. Bromus lanatipes (Woolly Brome)

Habit: A perennial species with distinctive woolly butt and leaf sheaths. Culms are 40–90 cm long, with pubescent culm nodes.
Inflorescence: An open, ovate panicle, 10–25 cm long, with ascending or spreading primary branches.
Fertile Spikelets: Oblong, laterally compressed, 10–30 mm long, with 6–8 fertile florets. They break up at maturity, disarticulating below each fertile floret.
Glumes: Persistent and shorter than the spikelet. The lower glume is lanceolate, 1–3-veined, and without keels. The upper glume is lanceolate, 3-veined, also without keels.
Florets: Fertile lemma is oblong (8–11 mm long), chartaceous, 5-veined, and without a keel. Its surface is pubescent, and the apex is awned (awn 2–4 mm long). The fruit is a caryopsis with an adherent, hairy apex.

3. Bromus catharticus (Rescue Grass)

Habit: A caespitose perennial, with culms erect or geniculately ascending, 80–100 cm long. Leaf sheaths are pubescent.
Inflorescence: An open, oblong, effuse panicle, 10–40 cm long, with flexuous branches.
Fertile Spikelets: Ovate, strongly laterally compressed, 16–40 mm long and 4–10 mm wide, containing 6–12 fertile florets. Rhachilla internodes are obscured by lemmas, and spikelets disarticulate below each fertile floret.
Glumes: Persistent and similar. The lower glume is lanceolate (10–15 mm long, 5–9-veined), and the upper glume is lanceolate (11–17 mm long, 9–13-veined), both chartaceous, 1-keeled, and with an acuminate apex.
Florets: Fertile lemma is oblong, distinctly keeled, 12–20 mm long, 3–7 mm wide, chartaceous, and 9–13-veined. The surface is scaberulous and rough on veins, with a lobed, 2-fid, awned apex (awn 1–9 mm long). The fruit is a caryopsis with an adherent, hairy, fleshy apex.

Genus Cynodon: Distinguishing Bermudagrass and Stargrasses

The genus Cynodon, including Bermudagrass and the Stargrasses, shows important differences in habit and inflorescence.

1. Cynodon nlemfuensis (Santo Domingo Stargrass)

Habit: A mat-forming perennial with stolons but no rhizomes. Culms are geniculately ascending (30–60 cm long), with stiff or firm mid-green or glaucous leaf blades.
Inflorescence: Composed of 4–8(–13) digitate racemes, straight or flexuous, unilateral, 4–7(–10) cm long. Spikelets are sessile and packed broadside to the rhachis in 2 rows.
Fertile Spikelets: Ovate, strongly laterally compressed, 2–3 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Lower glume is lanceolate, 1-keeled, 1-veined. Upper glume is lanceolate, 1-keeled, 1-veined.
Florets: Fertile lemma is ovate, laterally compressed (2–3 mm long), cartilaginous, keeled, and 3-veined, with a pubescent or ciliate midvein. Apex is acute.

2. Cynodon plectostachyus (African Stargrass)

Habit: A mat-forming perennial with stolons but no rhizomes. Culms are geniculately ascending (30–90 cm long), with mid-green leaf blades (10–30 cm long) that are scabrous and pilose.
Inflorescence: Features 7–20 digitate racemes, in several whorls, incurved, unilateral, 3–7 cm long. Spikelets are sessile and packed broadside to the rhachis in 2 rows.
Fertile Spikelets: Ovate, strongly laterally compressed, 2.5–3 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Lower glume is ovate (0.2–0.3 mm long), 1-keeled, 1-veined. Upper glume is ovate (0.4–0.6 mm long), 1-keeled, 1-veined.
Florets: Fertile lemma is ovate, laterally compressed (2.5–3 mm long), cartilaginous, keeled, and 3-veined, with a ciliate midvein. Apex is acute.

3. Cynodon dactylon (Bermudagrass)

Habit: A mat-forming perennial with both rhizomes and stolons. Culms are geniculately ascending (8–40 cm long), with glaucous leaf blades (1–12 cm long).
Inflorescence: Comprises 4–6 digitate racemes, unilateral, 1.5–6(–8) cm long. Spikelets are sessile and packed broadside to the rhachis in 2 rows.
Fertile Spikelets: Ovate, strongly laterally compressed, 2–2.5 mm long, with 1 fertile floret.
Glumes: Persistent, similar, and shorter than the spikelet. Lower glume is lanceolate, 1-keeled, 1-veined. Upper glume is lanceolate, 1-keeled, 1-veined.
Florets: Fertile lemma is ovate, laterally compressed (2–2.5 mm long), cartilaginous, keeled, and 3-veined, with a pubescent midvein. Apex is acute.

Genus Paspalum: A Look at the Carpetgrasses

Paspalum species are often characterized by their raceme inflorescences and plano-convex spikelets.

1. Paspalum notatum (Bahiagrass)

Habit: A mat-forming perennial with elongated rhizomes. Culms are 15–50 cm long, with spreading leaf blades.
Inflorescence: Typically 2 (sometimes 3) paired, unilateral racemes, 2.5–12 cm long. Spikelets are pedicelled and packed abaxially in 2 rows.
Fertile Spikelets: Elliptic, dorsally compressed, plano-convex, obtuse, 2.5–3.8 mm long, falling entire.
Glumes: Lower glume absent or obscure. Upper glume is ovate, cartilaginous, 3-veined, without keels, with an obtuse apex.
Florets: Fertile lemma is ovate, gibbous (2–3 mm long), indurate, pallid, striate, and without a keel, with an obtuse apex. Margins are involute.

2. Paspalum dilatatum (Dallisgrass)

Habit: A caespitose perennial with basal innovations. Culms are 40–180 cm long.
Inflorescence: Features (2–)3–5(–11) racemes borne along a central axis, unilateral, 4–11 cm long. Spikelets are in pairs, both sessile and pedicelled, packed in 2–4 rows.
Fertile Spikelets: Ovate, dorsally compressed, plano-convex, acute, 2.8–3.8 mm long, falling entire.
Glumes: Lower glume absent or obscure. Upper glume is ovate, membranous, yellow, 3-veined, pilose, with ciliate margins and an acute apex.
Florets: Fertile lemma is ovate, gibbous (2.5–3 mm long), indurate, pallid, striate, and without a keel, with an obtuse apex. Margins are involute.

3. Paspalum plicatulum (Brown-top Paspalum)

Habit: A caespitose perennial with short rhizomes. Culms are erect or geniculately ascending, 30–120 cm long. Leaf blades are flat or conduplicate.
Inflorescence: Consists of 2–7 racemes borne along a central axis, unilateral, 2–15 cm long. Spikelets are in pairs, pedicelled, and packed in 2–4 rows.
Fertile Spikelets: Elliptic or obovate, dorsally compressed, plano-convex, obtuse, 2.3–3.2 mm long, falling entire.
Glumes: Lower glume absent or obscure. Upper glume is ovate, membranous, 5-veined, without keels, with an obtuse apex.
Florets: Fertile lemma is ovate, gibbous (2–3 mm long), indurate, dark brown, and without a keel. Its surface is granulose, and margins are involute.

4. Paspalum atratum (Atra Paspalum)

Habit: A perennial with elongated rhizomes. Culms are robust, erect or geniculately ascending, 100–150 cm long.
Inflorescence: Composed of 10–16 racemes borne along a central axis, unilateral, 3–10 cm long. Spikelets are in pairs and pedicelled, packed in 4 rows.
Fertile Spikelets: Elliptic or obovate, dorsally compressed, plano-convex, 2–3 mm long, falling entire.
Glumes: Lower glume absent or obscure. Upper glume is elliptic, membranous, 5-veined, without keels.
Florets: Fertile lemma is elliptic (2–3 mm long), indurate, dark brown, shiny, and without a keel. Its surface is smooth, and margins are involute.

Genus Brachiaria: Signal and Humid Grasses

Brachiaria species are often distinguished by their hairy ligules and characteristic spikelet structures.

1. Brachiaria brizantha (Signalgrass)

Habit: A caespitose perennial, with culms erect or geniculately ascending, 30–200 cm long. Ligule is a fringe of hairs.
Inflorescence: Racemes (1–)2–16 borne along a central axis, unilateral, 4–20 cm long. Spikelets are solitary and sessile, packed in 1 row.
Fertile Spikelets: Elliptic, dorsally compressed, 4–6 mm long, falling entire. Spikelet callus is square.
Glumes: Dissimilar. Lower glume is ovate, clasping, 7–11-veined. Upper glume is oblong, cartilaginous, 7–9-veined.
Florets: Fertile lemma is elliptic (3.5–5.5 mm long), indurate, granulose, and without a keel. Margins are involute.

2. Brachiaria decumbens (Suriname Grass)

Habit: A perennial with stolons. Culms are decumbent, 50–150 cm long, wiry. Ligule is a fringe of hairs.
Inflorescence: Racemes 2–7 borne along a central axis, unilateral, 1–5 cm long. Rhachis is broadly winged and ciliate on margins. Spikelets are solitary and sessile, packed in 2 rows.
Fertile Spikelets: Elliptic, dorsally compressed, 4–5 mm long, falling entire. Spikelet callus is square.
Glumes: Dissimilar. Lower glume is ovate, clasping, 9-veined. Upper glume is oblong, membranous, 7-veined, pubescent.
Florets: Fertile lemma is elliptic (3.5–4.5 mm long), indurate, granulose, and without a keel. Margins are involute.

3. Brachiaria dictyoneura (Dictyoneura Grass)

Habit: A caespitose perennial without stolons. Culms are 40–100 cm long, without nodal roots. Ligule is a fringe of hairs.
Inflorescence: Racemes 3–8(–12) borne along a central axis, unilateral, 1–8 cm long. Rhachis is narrowly winged. Spikelets are solitary and sessile, packed in 2 rows.
Fertile Spikelets: Elliptic, dorsally compressed, 4–6 mm long, falling entire.
Glumes: Similar. Lower glume is oblong, 11-veined, pubescent. Upper glume is oblong, membranous, 7–9-veined, with cross-veins and a pubescent surface.
Florets: Fertile lemma is elliptic (3.5–5.5 mm long), indurate, papillose, and without a keel. Margins are involute.

4. Brachiaria humidicola (Humidicola Grass)

Habit: A perennial with stolons. Culms are geniculately ascending or decumbent, 40–100 cm long, rooting from lower nodes. Ligule is a fringe of hairs.
Inflorescence: Racemes 2–3(–4) borne along a central axis, unilateral, 2–7 cm long. Rhachis is wingless or narrowly winged. Spikelets are solitary and sessile, packed in 2 rows.
Fertile Spikelets: Elliptic, dorsally compressed, 4–6 mm long, falling entire.
Glumes: Similar. Lower glume is oblong, 11-veined, glabrous or pubescent. Upper glume is oblong, membranous, 5–9-veined, with cross-veins and a glabrous or pubescent surface.
Florets: Fertile lemma is elliptic (3.5–5.5 mm long), indurate, papillose, and without a keel. Margins are involute.

5. Brachiaria ruziziensis (Ruzi Grass)

Habit: A perennial with short rhizomes. Culms are decumbent, 50–100 cm long, rooting from lower nodes. Leaf blades are lanceolate (10–25 cm long), pilose on both sides with scabrous, cartilaginous margins.
Inflorescence: Racemes (3–)5–7(–9) borne along a central axis, unilateral, 5–10 cm long. Rhachis is broadly winged and ciliate on margins. Spikelets are solitary and sessile, packed in 2 rows.
Fertile Spikelets: Elliptic, dorsally compressed, cuspidate, 4–5 mm long, falling entire. Spikelet callus is square.
Glumes: Dissimilar. Lower glume is oblate, clasping, 11–13-veined. Upper glume is oblong, membranous, 7-veined, pilose with hairs above.
Florets: Fertile lemma is elliptic (4.5–5 mm long), indurate, striate, and without a keel. Margins are involute. The apex is apiculate.

Genus Lolium: Ryegrasses

Lolium species are notable for their single raceme inflorescence and laterally compressed spikelets.

1. Lolium multiflorum (Italian Ryegrass)

Habit: An annual, caespitose grass, with culms erect or decumbent, 30–90 cm long. Features falcate leaf-sheath auricles.
Inflorescence: A single, bilateral raceme, 10–30 cm long. Spikelets are sessile, appressed, and packed adaxially in 2 rows.
Fertile Spikelets: Oblong, laterally compressed, 7.5–25 mm long, with 5–15 fertile florets. Disarticulation occurs below each fertile floret.
Glumes: Lower glume absent or obscure. Upper glume is lanceolate, coriaceous, 4–7-veined, without keels, with a smooth surface and an obtuse or acute apex.
Florets: Fertile lemma is oblong (5–8 mm long), coriaceous, 5-veined, and without a keel. Its apex is dentate, 2-fid, obtuse, and awned (awn 5–10 mm long). Palea keels are scaberulous.

2. Lolium perenne (Perennial Ryegrass)

Habit: A perennial, caespitose grass, with culms erect or decumbent, 30–90 cm long. Features falcate leaf-sheath auricles.
Inflorescence: A single, bilateral raceme, 4–30 cm long. Spikelets are sessile, appressed, and packed adaxially in 2 rows.
Fertile Spikelets: Oblong, laterally compressed, 7–20 mm long, with 4–14 fertile florets. Disarticulation occurs below each fertile floret.
Glumes: Lower glume absent or obscure. Upper glume is lanceolate, coriaceous, 5–7-veined, without keels, with a smooth surface and an obtuse apex.
Florets: Fertile lemma is oblong (5–7 mm long), coriaceous, 5-veined, and without a keel. Its apex is obtuse and muticous. Palea keels are scaberulous.

Comparative Analysis: Key Distinctions

Understanding the differences between grass species is crucial for identification. For instance, Bromus carinatus has strongly compressed spikelets and a keeled fertile lemma, unlike Bromus lanatipes which has unkeeled glumes and lemma. Among Cynodon species, Cynodon dactylon is unique for possessing rhizomes in addition to stolons, whereas Cynodon nlemfuensis and Cynodon plectostachyus only have stolons. These subtle yet significant differences highlight the importance of detailed botanical descriptions.

Frequently Asked Questions (FAQ) about Grass Species Botanical Descriptions

What are the key parts used in botanical descriptions of grass species?

Botanical descriptions of grass species typically focus on the habit (growth form), inflorescence structure (how flowers are arranged), fertile spikelets (the basic unit of the grass inflorescence), glumes (bracts enclosing the florets), and florets (individual flowers including lemma, palea, and reproductive organs).

How do spikelets differ among various grass species?

Spikelets vary significantly in size, shape (elliptic, ovate, oblong), compression (laterally or dorsally), number of fertile florets, and how they disarticulate at maturity (e.g., falling entire or breaking up below each floret).

What role do glumes play in grass identification?

Glumes are important for identification based on their persistence, similarity, length relative to the spikelet, texture, presence or absence of keels, vein count, and apex shape. For example, some species have an absent or obscure lower glume.

What is a fertile lemma, and why is it important?

A fertile lemma is a key bract enclosing the fertile floret. Its characteristics, such as length, texture (herbaceous, chartaceous, coriaceous, indurate, cartilaginous), presence of a keel, vein count, surface texture (smooth, pubescent, scaberulous), and apex (awned, muticous, dentate, lobed), are critical for distinguishing different grass species. The lemma awn's length and position are also vital features. Learn more about grass morphology on Wikipedia.

Grass Species Botanical Descriptions