Grass Morphology: Part - I

Aeluropus lagopoides (L.) Thwaites

Habit

    Usually, grasses are herbaceous annuals or perennials; culms are usually hollow, occasionally with pith-filled solid internodes. Annuals are characterized by shallow roots and will emerge at the onset of the monsoon and produce flowers and fruits at the end of the season and perish. Whereas in perennials, roots are deep and have dormant buds or innovation shoots at the base, and with the advent of favorable conditions they sprout and produce culms, flowers, and fruits. 

Tripogon bromoides Roth

Spodiopogon rhizophorus (Steud.) Pilg.

Root system

    Usually, grasses have a fibrous root system but occasionally, they have woody rootstock, rhizomatous and stoloniferous rootstock which remains dormant in unfavorable conditions. Rhizomes (underground stem) and stolons (horizontal above-ground branches) help in vegetative reproduction in perennial grasses. Some grasses like Chionachne koenigii, Sorghum halepense, Spodiopogon rhizophorus, Rottboellia cochinchinensis, posses stilt roots. In few marshy and coastal grasses, roots form into mats. In aquatic floating grass, Hygroryza aristata roots are numerous and feathery, enabling them to float on water. 

Culms

    Stems in grasses are generally referred to as culms, they are erect, decumbent, or creeping having nodes and internodes. Nodes are generally solid offering support to the grass and small in size, either glabrous or hairy, leaf sheath emerges from it. Internodes are usually hollow, longer than nodes, partially or completely covered by leaf sheath. In aquatic grass, Hygroryza aristata culms are spongy. In Saccharum officinarum (Sugar cane), internodes are filled with juicy pith containing sucrose. Grasses have intercalary meristems which allow culms to resprout near the base after repeated episodes of fire or grazing. 

Leaves

    Grass foliage is divided into two parts, leaf-sheath, and leaf-blade which is separated by ligule. Leaf-sheath emerges from nodes and partially or completely clasps internodes. In some grasses, leaf sheaths are covered with tubercle-based, glandular, or simple hairs either sparsely or densely. In Chionachne koenigii, leaf sheaths are covered with stiff, hairs. Ligules are membranous or hairy rim present at the junction of leaf blades and leaf sheaths. The function of the ligule is to block water from getting into the leaf sheath. In a few grass species, it is absent (eligulate). The leaf blades are varied in shape, size, and indumentation; it varies from filiform to linear-lanceolate to broadly ovate, obovate, oblong. It can be a few centimeters to several feet. In genera like Tripogon, Eragrostiella, the leaf blades are filiform. In grasses like Centotheca, Oplismenus spp. and Ichnanthus spp. leaf blades are broadly ovate to lanceolate. Grasses inhabiting the shade of the forest trees have a thin texture compared to the grasses that grow in the open area having a thick texture.

Setaria pumila (Poir.) Roem & Schult.

Eragrostis tenella (L.) P. Beauv. ex Roem. & Schult.

Chloris barbata Sw.

Inflorescence

    Grasses exhibit various types of inflorescence. Some grasses have solitary spikes viz. species belonging to the genera Eragrostiella, Tripogon, Microchloa, etc. In this case, inflorescence consists of a single spike with alternately arranged spikelets (Eragrostiella, Tripogon) or towards one side (Microchloa) spikelets are either pedicelled or sessile. Genera like Chloris, Digitaria, Eleusine, Dactyloctenium, Dimeria have digitate spikes. In this type, the spikelets are arranged in spikes that are digitately arranged. In Arundinella, Panicum, Eragostis, etc. panicle type of inflorescence are seen, here the main axis divides into many lateral branches and lateral branches are further divided, these divided branches forms a panicle, spikelets are either solitary or paired. Species belonging to the genera Apluda, Themeda, Iseilema, etc, have compound panicle or false panicle where racemes are subtended by spathes and spatheoles. Some species of Setaria and Pennisetum, have cylindrical panicles, here spikelets are arranged on the main central axis, either sessile or pedicelled. Some genera belonging to Andropogoneae like Dichanthium, Arthraxon, Ischaemum, Andropogon, etc., have digitate racemes where spikelets are arranged on digitate racemes; the spikelets are paired, one sessile other pedicelled. In genera like Sehima, Apocopis, etc., the inflorescence is a spike-like raceme, where spikelets are arranged on the central axis; they are either paired or solitary, if paired, one sessile and other pedicelled.

    

Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult.

Apluda mutica L.

    

    Most of the grass spikelets have both male and female florets. But with a few exceptions like Chionachne, Coix and Zea, which are monoecious, having male and female spikelets borne at different positions in the same plant. In Chionachne koenigii and Coix lacryma-jobi male and female florets are in the same inflorescence. In Zea mays, both male and female spikelets are in separate inflorescence on the same plant. Spinifex littoreus is dioecious, where male and female plants are separate.