I. SYNONYMS: monocots

II. NUMBER: >50,000 extant species

III. CHARACTERISTICS OF THE CLASS

• A. Structure
  • Habit: Variable; these plants range from herbaceous to woody, but they have no active cambium. The monocots are seed plants which bear flowers and fruits. The embryos are monocotyledonous.
  • Flowers: The floral parts tend to be in sets of 3.
  • Pollen: Pollen walls are variable, but they usually have 1 aperture. The microgametophyte has no prothallial cells or stalk cells and contains only 2 nonflagellate sperms and a tube cell.
  • Seeds: Ovules borne in a fruit (matured ovulary). Thus pollen tube must grow to the micropyle. The megagametophyte is greatly reduced, often of only 7 cells. Double fertilization produces the embryo and the endosperm. The embryo is monocotyledonous.
  • Stems: Atactostelic, monocots have vascular bundles scattered through a common cortex. Xylem contains vessels.
  • Leaves: Usually parallel-veined blade with a basal sheath and no petiole.
  • Roots: Adventitious.

• B. Ecology: Very abundant, the monocots have exploited almost every terrestrial and aquatic (not marine) habitat on this planet. Their fossil history dates back to the end of the Cretaceous period.

SUBCLASS ALISMATIDAE

These plants typically inhabit wetland or aquatic environments and are herbaceous. Generally apocarpous. They have trinucleate pollen. Mature seeds lack endosperm. The fossil history extends back 60 million years, at the beginning of the Tertiary period. This subclass has 4 orders (I give only 1 here).

• ORDER ALISMATALES
  • Perennial aquatic or semi-aquatic herbs. Much aerenchyma. Xylem sparsely lignified; vessels confined to roots. Vascular bundles scattered or in 2 concentric rings. Leaves alternate and clustered at the tip of the rhizome; somewhat ensheathing at the base; sometimes differentiated into petiole and blade. Inflorescence usually cymes or racemes (rarely solitary). Flowers actinomorphic and 3-merous (3 green sepals and 3 white petals); stamens 3-many. Pollen usually with many pores. Gynoecium of 3-20 apocarpous (separate or unfused) pistils, each with 1-many ovules. This order contains 3 families, of which Alismataceae is the representative family.
  • Alisma, Echinodorus, Sagittaria.

SUBCLASS ARECIDAE

Herbaceous or woody trees or shrubs. Woody species with limited secondary growth which does not lead to new vascular tissue. Vessels can be present in all plant organs. Leaves alternate, or with short internodes to become all basal or all terminal in a crown. Blades palmate, pinnate or simple, often very large; net or parallel-veined. Flowers crowded and usually small, often borne in a spadix. Perianth usually small and in 2 series of 3 tepals. Flowers imperfect or perfect. Plants sometimes dioecious. Stamens 1-many; pollen grains usually binucleate; usually with 1 aperture. Gynoecium usually of 3 carpels, usually fused. Ovules 1-many in each locule. Endosperm oily and often copious. Fruit a berry or drupe. Embryo monocotyledonous. The fossil history of this group extends back to the upper Cretaceous period. This subclass has 4 orders (I present 2 here).

• ORDER ARECALES
  • Mostly slender trees or stout shrubs with an unbranched trunk covered by persistent leaf bases. Leaves evergreen, alternate and very large with a basal sheath, a petiole and an expanded pinnately parallel blade. The blade may be either pinnately or palmately compound, no axillary buds. Inflorescenses large, paniculate and subtended by 1 or more spathes. Flowers perfect or imperfect; monoecious or dioecious. Flowers actinomorphic; 3 sepals and 3 petals; 6 stamens in 2 series of 3. Gynoecium a compound pistil of 3 fused carpels. Fruits berries or drupes. Endosperm large and embryo very small. This order has only 1 family, the Arecaceae (Palmae).
  • Areca, Lodoicea, Cocos, Phytelephas, Elaeis, Calamus, Sabal, Phoenix, Serenoa, Washingtoia, Copernicia, Metroxylon, Coccothrinax, Roystonea.

• ORDER ARALES
  • Usually herbs, rarely vines or shrubs. Leaves alternate, basal. Petiole sheathing and the leaf blade expanded with reticulate or net veins. Inflorescence a spadix subtended by a spathe with tiny perfect or imperfect flowers. Perianth often tiny or missing. Pollen grains 2-3 nucleate and usually 1 aperture. Gynoecium of 3 fused carpels. Fruit a berry or a multiple. Embryo large in copious oily endosperm. This order has 2 families, of which Aracaceae is the representative family.
  • Acorus, Aglaonema, Anthurium, Arisaema, Calla, Caladium, Colocasia, Dieffenbachia, Lysichiton, Orontium, Peltandra, Philodendron, Pistia, Spathiphyllum, Symplocarpus.

SUBCLASS COMMELINIDAE

Herbs (some somewhat woody) without secondary growth. Vessels usually present in all vegetative organs. Leaves alternate, simple and entire; parallel-veined; with a basal sheath and a broader blade. Flowers hypogynous; perfect or imperfect. Perianth 3-merous or reduced and chaffy or bristly. Stamens, 3 or 6. Pollen grains either binucleate or trinucleate; uniaperturate. Gynoecium of 2 or 3 fused carpels; ovules 1-many. Fruit usually dry; endosperm starchy. The fossil history of this group extends to the upper Cretaceous period. This subclass has 7 orders (I present one order here).

• ORDER CYPERALES
  • Perennial herbs (rarely annual); sometimes woody, but always without secondary growth. Cell walls often contain silica. Leaves in 2 or 3 ranks with a basal sheath and a narrow parallel-veined blade; an adaxial ligule is usually present at the junction of the sheath and blade. Flowers very small and organized into spikes or spikelets which are organized into secondary inflorescences. Flowers perfect or imperfect; enclosed between a pair of scales. Pollen grains trinucleate and with one aperture. This order has 2 large families, of which the Poaceae (Gramineae) is the representative family. This is an enormous family that includes the most economically important food species (sugar cane and almost all of the grains; these are indicated in blue). The family is so large that I have listed the following genera according to subfamily.
  • Bromus, Festuca, Poa, Dactylis, Lolium, Vulpia, Spenopholis, Trisetum, Aira, Avena, Holcus, Calamagrostis, Agrostis, Polypogon, Cinna, Anthoxanthum, Phalaris, Alopecurus, Phleum, Elymus, Hordeum, Triticum, Secale, Sitanion, Hystrix, Agropyron, Melica, Glycera, Catabrosa, Schizachne, Stipa, Oryzopsis, Piptochaetium, Brachyelytrum, Diarrhena, Nardus, Monerma, Parapholis.
  • Digitaria, Leptoloma, Anthaenantia, Stenotaphorum, Brachiaria, Axonopus, Eriochloa, Paspalum, Panicum, Opilsmenus, Echinolochia, Sacciolepis, Rhynchelytrum, Setaria, Pennisetum, Cenchrus, Amphicarpum, Imperata, Miscanthus, Saccharum, Erianthus, Sorghum, Sorgastrum, Andropogon, Arthraxon, Dicanthium, Bothriochloa, Schizachyrium, Eremochloa, Heteropogon, Manisuris, Tripsacum, Zea, Coix.
  • Eragrostis, Tridens, Triplasis, Erioneuron, Munroa, Redfeldia, Calamovilfa, Lycurus, Spropbolus, Muhlenbergia, Blepharoneuron, Eleusine, Dactyloctenium, Leptochloa, Gymnopogon, Tripogon, Ctenium, Hilaria, Schedonardus, Cynodon, Chloris, Trichloris, Bouteloua, Buchloe, Cathestecum, Aegopogon, Tragus, Spartina, Zoysia, Distichlis, Allolepis, Monanthochloe, Uniola, Pappophorum, Enneapogon, Cottea, Orcuttia, Neostapfia, Aristida.
  • Arundinaria, Bambusa, Schizostachyum, Pharus.
  • Oryza, Leersia, Zizania, Zizaniopsis, Luziola, Hydrochloa.
  • Arundo, Phragmites, Cortaderia, Molinia, Danthonia, Schismus, Chasmanthium.

SUBCLASS ZINGIBERIDAE

Herbs, often epiphytic, some terrestrial. Vessels restricted to the roots. Leaves basal with a sheathing base and blade with parallel or pinnate-parallel veins. Inflorescence usually with showy bracts. Flowers variable; 3-merous (3 sepals, 3 petals, 6 stamens). Pollen variable, bi- or trinucleate; 1 to many pores. Gynoecium usually of 3 fused carpels; epigynous. Fruit a capsule or false berry (sometimes multiple). Endosperm starchy. This subclass has 2 orders.

• ORDER BROMELIALES
  • Usually epiphytic herbs (sometimes terrestrial). Leaves alternate and forming a rosette, many of which are adapted to collecting rain water. Flowers perfect, well adapted to insect pollination. Pollen with 2-3 pores. Fruit usually fleshy (a berry) or a capsule. Embryo variable, small to large; wsith copious, mealy endosperm. This order has a single family, Bromeliaceae.
  • Navia, Pitcairnia, Puya, Bromelia, Ananas, Tillansia.

• ORDER ZINGIBERALES
  • Perennial herbs from large, often starch rhizomes. Leaves opposite or spiraled; often parallel-pinnate with a distinct petiole. Inflorescences usually subtended by bracts; perfect or imperfect. Stamens 6, although rarely are all 6 functional. Gynoecium often of 3 fused pistils. Fruit variable; dry or fleshy; dehiscent or indehiscent. Seeds with endosperm and copious, starchy perisperm. This order has 8 families, of which the Musaceae is a representative family.
  • Musa.

SUBCLASS LILIIDAE

The flowers are syncarpous with showy sepals and petals (3-merous). Well adapted to insect pollination. Mainly terrestrial, geophytes or epiphytes. Leaves are usually linear and parallel-veined; usually alternate (sometimes all basal); with or without a sheathing leaf base. Flowers actinomorphic to zygomorphic and usually perfect; stamens usually 1,3 or 6. Gynoecium of 3 fused carpels; epigynous or hypogynous. Fruits usually capsular, sometimes fleshy. The fossil history of this group extends to the upper Cretaceous period. This class has 2 very large orders, both of which are presented here.

• ORDER LILIALES
  • Usually geophytic perennial herbs. Vessels confined to the roots. Leaves usually simple and entire. Tepals in 2 series of 3. Usually as many stamens as tepals. Pollen binucleate and mono sulcate. Gynoecium epigynous or hypogynous; usually of 3 fused carpels. Fruit usually a capsule but often a berry or drupe. Seeds with abundant endosperm (hemicellulose, oil and protein). This order has 15 families, of which Liliaceae is the representative family.
  • Allium, Aloe, Lilium, Asparagus, Calochortus, Camassia, Clintonia, Colchicum, Convallaria, Erythronium, Fritillaria, Hemerocallis, Kniphofia, Medeola, Muscari, Polygonatum, Scilla, Smilacina, trillium, Tulipa, Uvularia, Veratrum.

• ORDER ORCHIDALES
  • Usually epiphytic, geophytic ot terrestrial herbs. They are strongly mycotrophic. Leaves usually with an ensheathing leaf base; but sometimes the leaf is highly modified. Flowers usually strongly zygomorphic, epigynous; 3-merous; often with only 1-2 stamens. Pollen binucleate and monosulcate (or exine lacking entirely). Gynoecium of 3 fused carpels; the fruit is capsular. Seeds are very numerous and tiny, without endosperm; embryo usually of only a few cells (thus, usually cotyledon undifferentiated). This order has 4 families, of which the Orchidaceae is the representative family. Orchidaceae is a very large and diverse family (~735 genera and >17,000 species). Thus, I have organized the following representative genera according to subfamily groupings.
  • Apostasia.
  • Cypripedium.
  • Epipactis, Goodyera, Listera, Spiranthes.
  • Habenaria, Orchis.
  • Cleistes Isotria, Pogonia, Vanilla.
  • Calopogon, Cattleya.
  • Liparis, Malaxis.
  • Aplectrum, Corallorhiza, Cymbidium, Tipularia.