Monocots Cajsa Lisa Andersona,* and Thomas Janßenb represent an adaptation to shaded habitats such as the aDepartment of Biodiversity and Conservation, Real Jardin Botanico, forest understorey. CSIC, Plaza de Murillo 2, 28014 Madrid, Spain; bResearch Institute Acorales is a small wetland order, consisting of only Senckenberg, Department of Botany and Molecular Evolution, one genus, Acorus (sweet P ag). 7 e small P owers are Senckenberganlage 25, 60325 Frankfurt, Germany densely placed on a thick axis forming a spadix. 7 is *To whom correspondence should be addressed (cajsa.lisa. [email protected]) inP orescence produces a strong odor attracting pollina- tors. 7 e plants possess ethereal oils in specialized cells. 7 e Order Alismatales contains 14 families, which all Abstract have a preference for aquatic or wetland habitats. 7 ey possess stems with small scales or glandular hairs within Grasses, lilies, orchids, and many other plants from all bio- the sheathing leaves at the nodes, extrorse anthers, and geographical and climatic regions of the world constitute a large embryo. Araceae, or the arum family (Fig. 1), the monocotyledonous plants (monocots). They form a nat- includes the calla lily and taro. 7 e inP orescence of ural group of about 59,300 species in 81 families supported these plants is a spadix, which is surrounded by a leaf- by morphological and molecular evidence and include like bract. 7 e small P oating duckweeds, Lemna and many important crops, such as rice and corn, and orna- other genera, have previously been segregated into the mental plants. Previous analyses and new analyses pre- Family Lemnaceae, but are recognized as part of Araceae sented here suggest a rapid radiation of all major monocot by APGII (2). Alismataceae, or the water plantains, lineages during the Early Cretaceous (146–100 million years have comparatively large P owers and usually two- to ago, Ma). Most extant monocot families were present at the polyporate pollen. 7 e embryo is strongly curved, and Mesozoic–Cenozoic boundary (66 Ma). 7 e monocots are a strongly supported monophyletic group comprising about 25% of the angiosperm diver- sity. 7 ey number 59,300 species (1) and are classiA ed in 81 families and 10 orders by the Angiosperm Phylogeny Group (APGII) (2). A number of morphological charac- ters are shared by most monocots, although these may have been (secondarily) lost in some lineages. 7 e single cotyledon, leaves with linear venation, a basal meristem, scattered vascular bundles in the shoots and a lack of secondary growth of xylem and phloem, and sieve cell plastids are among the most obvious shared-derived morphological characters. Monocots usually possess tri- merous P owers and uniaperturate pollen, which is most commonly monosulcate. Monocot characters also appear in other angiosperm groups. For example, sieve cell plas- tids occur in some Aristolochiaceae, scattered vascular Fig. 1 Monocot representatives. Top row, from left to right: bundles in Nymphaeaceae and some Piperaceae, and tri- Cypripedium calceolus L., Orchidaceae; Convallaria majalis L., Asparagaceae, with a straw of Carex digitata L., Cyperaceae. merous P owers with two perianth whorls are present in Bottom row, from left to right: Dracunculus muscivorus Parl., Nymphaeaceae and some magnoliids. Several monocots Araceae; Tillandsia usneoides L., Bromeliaceae; Cynosurus from diB erent orders and families do have reticulate ven- cristatus L., Poaceae. Credits: Ola Lundström (Dracunculus) ation. 7 is is, however, a derived condition thought to and C. L. Anderson (all other images). C. L. Anderson and T. Janßen. Monocots. Pp. 203–212 in e Timetree of Life, S. B. Hedges and S. Kumar, Eds. (Oxford University Press, 2009). HHedges.indbedges.indb 220303 11/28/2009/28/2009 11:26:43:26:43 PPMM 204 THE TIMETREE OF LIFE Poaceae 63 Ecdeiocoleaceae 62 Joinvilleaceae 40 Restionaceae 50 Anarthriaceae 32 48 Centrolepidaceae Flagellariaceae 24 Xyridaceae 36 20 Eriocaulaceae Poales Bromeliaceae Juncaceae 19 54 Cyperaceae 44 Thurniaceae 30 Typhaceae 59 21 Sparganiaceae Rapateaceae Zingiberaceae 71 Commelinids Costaceae 15 66 Marantaceae 73 Cannaceae Streliziaceae 70 Lowiaceae Zingiberales 61 Musaceae 60 12 Heliconiaceae 18 Pontederiaceae 53 Commelinaceae 43 11 Haemodoraceae 35 Hanguanaceae 27 Commelinales Philydraceae Dasypogonaceae Arecaceae (continued on next page) Early K Late KPaleogene Ng MESOZOIC CENOZOIC 10050 0 Million years ago Fig. 2 Continues the plants possess white latex. Hydrocharitaceae, tape anthers spreading pollen on the water surface, and under- grasses, occur in both freshwater and marine habitats. water pollination are just some examples. In Alismatales 7 e genera display several diB erent pollination mecha- we also A nd Potamogetonaceae, perennial herbs with nisms: showy P owers above water pollinated by nectar- either P oating or submerged leaves and oJ en jointed gathering insects, detached male P owers P oating on the stems, Zosteraceae (seagrasses) consisting of a dozen water surface until they meet a female P ower, exploding species with ribbonlike leaves and creeping rhizomes, HHedges.indbedges.indb 220404 11/28/2009/28/2009 11:26:45:26:45 PPMM Eukaryota; Viridiplantae; Streptophyta; Magnoliophyta; Monocots 205 (continued from previous page) Asparagaceae 51 Alliaceae 49 Xanthorrhoeaceae 10 42 Xeronemataceae 37 Iridaceae 34 Doryanthaceae 33 Tecophilaeaceae 22 14 Ixioliriaceae Orchidaceae Asparagales Hypoxidaceae 13 47 Blandfordiaceae 41 Asteliaceae 29 Boryaceae 28 Lanariaceae Colchiaceae 67 Alstroemeriaceae 6 65 31 Luzuriagaceae Melanthiaceae 23 Rhipogonaceae 68 Liliales Philesiaceae 57 Smilaceae 16 56 Liliaceae Campynemataceae (continued on next page) Early K Late KPaleogene Ng MESOZOIC CENOZOIC 100 50 0 Million years ago Fig. 2 Continues and a number of smaller families, oJ en with only one where the increase of trunk diameter is the result of pri- genus, or even one species. mary thickening growth. 7 e core monocots include the orders Dioscoreales, Liliales consists of 10 families, oJ en with showy P ow- Pandanales, Liliales, Asparagales and the commelinid ers, possessing tepals with basal nectaries. Liliaceae orders Zingiberales, Commelinales, and Poales. 7 e (tulips, lilies, and others) are herbaceous with bulbs or Families Petrosaviaceae (closest to the remainder of corms. 7 ey have actinomorphic, hypogynous P owers, the core monocots) and Dasypogonaceae (closest to the oJ en with various color patterns. Colchicaceae (autumn Commelinales + Poales + Zingiberales) are not placed crocus and naked ladies) are a family of mainly seasonal in any of the orders. Dioscoreales include the predom- perennials occurring in dry habitats in Africa and Eurasia, inantly tropical Family Dioscoreaceae, twining vines with a few exceptions conA ned to Australian rainforests with net-veined leaves, and with several members cul- and wet sclerophyllous forests. 7 e presence of the highly tivated for their edible starchy tubers, called yams. Two poisonous alkaloid colchicine is a synapomorphy of the other families belong to this order, Burmanniaceae and family. Within the Liliales we also A nd eight other fam- Nartheciaceae. Pandanales include the screw-pines, ilies, examples being Alstroemeriaceae, with a distribu- which are woody plants, branching trees, or shrubs, tion from Central America to southern South America, HHedges.indbedges.indb 220505 11/28/2009/28/2009 11:26:45:26:45 PPMM 206 THE TIMETREE OF LIFE (continued from previous page) 4 Velloziaceae 38 Stemonaceae 25 Pandanaceae 55 Cyclanthaceae Pandanales Dioscoreaceae 17 Burmanniaceae 9 Nartheciaceae Dioscoreales Petrosaviaceae Zosteraceae 75 72 Potamogetonaceae 2 Ruppiaceae 64 Posidoniaceae 69 58 Cymodoceaceae 46 Juncaginaceae Scheuzeriaceae 39 Aponogetonaceae 1 26 Hydrocharitaceae Alismatales 52 Butomaceae 45 5 Limnocharitaceae 74 Alismataceae 3 Tofieldiaceae Araceae Acoraceae Early K Late KPaleogene Ng MESOZOIC CENOZOIC 10050 0 Million years ago Fig. 2 A timetree of monocots. Divergence times are shown in Table 1. Abbreviations: K (Cretaceous) and Ng (Neogene). Campynemataceae, comprising a few species of peren- of families within the Asparagales are Iridaceae (e.g., nial herbs in New Caledonia and Tasmania, Corsiaceae, iris and saB ron), Xanthorrhoeaceae (grass-tress, aloe, which is a family of nonphotosynthesizing herbs and and asphodels), Alliaceae (onion, leek, and garlic), and Smilacaceae, with representatives that typically have Asparagaceae (asparagus, Lily-of-the-Valley (Fig. 1), aga- woody roots and a climbing or vining growth form. ves), the last two families now circumscribed to include a Asparagales, according to APGII, include a large num- number of previously recognized families (Fig. 1). ber of families. 7 eir actual number varies according to 7 e commelinids comprise about half of the species of the delimitation of individual families that is adopted. monocots, and include the orders Arecales, Zingiberales, Orchidaceae, the orchids (Fig. 1), is the second largest of Commelinales, and Poales. 7 e Arecales (palms) is a large all plant families with about 20,000 known species, the order of woody tree-like or rarely climbing plants with majority being epiphytes in tropical rainforests. Floral pinnately or palmately veined leaves and trunks with organization is relatively constant with two whorls of primary thickening growth. Zingiberales comprise large, tepals, and most oJ en a column consisting of a single sta- rhizomatous herbs with showy P owers. Well-known rep- men adnate to the style