Poaceae (Gramineae)

The Poaceae are mostly herbs comprising one of the largest families of flowering plants with about 500 genera and 8,000 species. The stems are round and commonly hollow, at least in the internodes. The leaves are alternate, and commonly 2-ranked, proximally comprising an open sheathing base with overlapping margins, and distally producing a parallel-veined, strap-shaped blade. On the adaxial leaf surface at the junction of the blade and sheath is an often hairy fringe of tissue called a ligule. The basic unit of the inflorescence is called a spikelet typically consisting of a basal pair of minute sterile bracts called glumes and one or more distichously arranged distal florets on an often zigzag extension of the spikelet axis called the rachilla. Each floret is typically embraced by an additional pair of minute chaffy bracts called the lemma and the palea. The florets are unisexual or bisexual and have usually two or three barely recognizable structures called lodicules that may represent a vestigial whorl of perianth that forces the lemma and palea apart during anthesis, thereby facilitating exsertion of the stamens and stigmas. The androecium typically consists of three or occasionally 6 distinct stamens. The gynoecium consists of a single compound pistil of 2 or sometimes 3 carpels, an equal number of styles with feathery stigmas, and a superior ovary with one locule containing a single subapical to basal ovule. The fruit is usually a caryopsis.

Each "thumbnail" image below is linked to a larger photograph.

Briza minor, quaking grass (Festucoideae-Poeae). Some of the florets in these three spikelets have the stamens exserted. Festucoid grasses commonly have more than one bisexual floret, and if they have any sterile florets, i.e. those without pistils, they are situated above one or more fertile florets. The florets of the spikelets are generally compressed from side to side rather than from front to back. When the spikelets mature and disintegrate, the glumes mostly remain on the plant.
Bromus willdenowii, rescue grass, Palehua-Palikea Tr., O'ahu, Hawai'i, 2003.
dac_glo_cus.jpg (10095 bytes) Dactylis glomerata, cocksfoot (Festucoideae-Poeae).  The spikelets are 3-6-flowered in this genus; in this species the lemma has a rigid awn up to 1.5 mm long.
Dactyloctenium aegyptium, beach wiregrass (Festucoideae-Eragrostideae)
ele_ind_cus.jpg (9889 bytes) ele_ind_fls.jpg (9238 bytes)
Eleusine indica, wiregrass (Festucoideae-Eragrostideae).  In this genus the inflorescences are digitate (not shown here - see Cynodon below).  Note the several-flowered, laterally compressed spikelets arranged in 2 imbricate rows..
era_sp_cus.jpg (9277 bytes) Eragrostis sp., lovegrass (Festucoideae-Eragrostideae).  Note laterally compressed spikelets.
spo_ind_frs.jpg (11902 bytes) Sporobolus, indicus, West Indian dropseed, smutgrass (Festucoideae-Eragrostideae).  This genus is characterized by have small, 1-flowered spikelets; the fruit usually falls free of the lemma and palea upon maturity.
cyn_dac_habs.jpg (8837 bytes)
Cynodon dactylon, Bermuda grass (Festucoideae-Cynodonteae). This genus often has digitate inflorescences with sessile spikelets in 2 rows; the spikelets have one basal fertile floret and often a terminal, sterile or vestigial floret.   Exserted yellowish stamens and reddish, feathery stigmas are clearly visible in the second photo. Pendulous stamens that produce copious, dry, thin-walled pollen and stigmas that are large and feathery are typical of wind pollinated plants and this is the most common mode of pollination among grasses.
chl_vir_cus.jpg (15250 bytes) Chloris virgata, feather fingergrass (Festucoideae-Cynodonteae).  This genus has digitate inflorescences; the spikelets are secund in 2 rows, awned, bearing 1 basal, usually somewhat inflated fertile floret and 1-3 sterile distal florets. Note the persistent glumes typical of Festucoid grasses on the axis at the left of the photo.
bra_sub_cus.jpg (5389 bytes) Brachiaria subquadripara (Panicoideae-Paniceae).  Note smooth, awnless spikelets.
Cenchrus echinatus, sand bur (Panicoideae-Paniceae). In this case the florets are enclosed by a cluster of numerous coalescing bristles that are very effective in aiding dispersal of the fruits by tangling in the fur of animals or feathers of birds.
dig_ins_cus.jpg (11623 bytes) Digitaria insularis, sourgrass (Panicoideae-Paniceae).  Note silky pubescent florets and disarticulation of spikelets below the glumes.
Melinus minutiflora, molasses grass (Panicoideae-Paniceae). The sterile lemma of each floret has a long awn up to 1.5 cm in length.
opl_com_cus.jpg (8855 bytes) Oplismenus compositus, (Panicoideae-Paniceae).  This genus has the spikelets in pairs; the glumes have awns up to 15 mm long.
pan_max_habs.jpg (13887 bytes) pan_max_cus.jpg (8369 bytes)
Panicum maximum, Guinea grass (Panicoideae-Paniceae). The panicoid grasses typically have small spikelets, commonly consisting of a single staminate or neuter floret at the base of the spikelet and a single bisexual, fertile, terminal floret. At maturity, the entire spikelet usually separates from the plant as a unit, including the glumes. Any compression of the florets in the spikelet is usually from front to back rather than from side to side.
pas_dil_cu2s.jpg (11605 bytes) Paspalum dilatatum, dallis grass (Panicoideae-Paniceae).  Note exserted stamens and stigmas.
pas_fim_cus.jpg (13030 bytes) Paspalum fimbriatum, Panama or fimbriate paspalum, Colombia grass (Panicoideae-Paniceae).  In this genus the spikelets are in two rows and they exhibit strong dorsi-ventral compression.  The lemma of the fertile (terminal) floret is indurate.  As in most Panicoid grasses, the florets separate from the axis below the glumes.
pen_pur_hab2s.jpg (14093 bytes) pen_purs.jpg (12724 bytes)
Pennisetum purpureum, elephant grass, napier grass (Panicoideae-Paniceae).   This robust species may reach 15 or more feet in height.  The spikelets are subtended by an involucre of numerous deciduous bristles up to 15 mm or longer.
set_gra_cus.jpg (12950 bytes) Setaria gracilis, yellow foxtail (Panicoideae-Paniceae).  The spikelets are subtended by 1-several persistent, scabrous-barbellate bristles; disarticulation of spikelets occurs between the glumes and the subtending bristles.
Coix lacryma-jobi, Job's tears, (Panicoideae-Andropogoneae). This maize relative is naturalized in Hawaii and is sometimes cultivated as an ornamental. The pearl-like accessory fruits are sometimes used for lei construction.
het_con_cus.jpg (8604 bytes) Heteropogon contortus, pili grass, twisted beardgrass, tanglehead (Panicoideae-Andropogoneae).  In this species each lemma may have an awn up to 12 cm long; these are often twisted together in the upper part of the inflorescence.
Saccharum officinarum, sugar cane (Panicoideae-Andropogoneae). Once a very important cash crop in Hawaii, cultivation of sugar cane is no longer economically rewarding.
sor_hals.jpg (4309 bytes)
Sorghum halepense, Johnson grass (Panicoideae). This particular tribe (Andropogoneae) of panicoid grasses typically has the spikelets in pairs (1 stalked, 1 sessile) along the axis. Both Panicoid and Festucoid grasses typically have a flap of tissue called a ligule at the junction of the blade and sheathing portion of the leaf. In this case the sheathing portion of the leaf has been pulled away from the stem to make the ligule more visible. A fringe of hairs is often associated with the ligule.
Phragmites sp., (Arundinoideae)
Coraderia selloana, (Arundinoideae)
Oryza sativa, rice (Oryzoideae). This species is one of the most important food crops that humans utilize, providing the primary source of starch for a large segment of the world's population.
bamboo, (Bambusoideae). The bamboos are the only woody members of the grass family. They also combine the most primitive characters occurring within the family, such as florets with six stamens, and tricarpellate pistils.
Bambusa cf. vulgaris, bamboo.
Gigantochloa verticillata, bamboo (Bambusoideae). Note the comparatively large spikelet, and florets with six exserted stamens.

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