**1. Introduction**

70 The Dynamical Processes of Biodiversity – Case Studies of Evolution and Spatial Distribution

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The role of Systematics in studies of biodiversity is essential to a variety of studies, including species conservation, extinction, biodiversity hotspots, bio-prospecting and ecosystem function (Alroy, 2002; Scotland & Wortley, 2003; Smith & Wolfson, 2004; Wilson, 2000). The analysis of the biodiversity as well as the analysis of the distribution of species richness at different levels (national, regional), the distribution of the endemic species, the detection of areas whose preservation is necessary and many other topics related to the conservation of the biodiversity requires an important collection effort, so that the organized databases constructed by the herbaria become as comprehensive as possible. Herbarium specimens represent a rich source of information for botanists and ecologists, even though data based on herbaria collections have many limitations, since they are geographically and seasonally biased, and taxonomically incomplete (Crawford & Hoagland, 2009; Delisle et al., 2003; Fuentes et al., 2008; Funk & Richardson, 2002; Ponder et al., 2001). Moreover, it has been established that there is a tendency to a decline in the number of specimens of vascular plants collected in the last years (Prather et al., 2004), although taxonomists are aware that there are still many undescribed species (Smith & Wolfson, 2004). In order to know how many species of grasses exist in Chile, as well as their identity and taxonomic distribution, this chapter provides a checklist of the family Poaceae in Chile, taking into account the nomenclatural changes recently proposed. Moreover, we analyze the completeness of the inventory of the family represented in two of the most important national herbaria.

Grasses (Poaceae or Gramineae) are the fifth most diverse family among the flowering plants or Angiosperms and the second most diverse family among the Monocotyledons. Poaceae comprises about 10,000 species in approximately 700 genera (Clayton & Renvoize, 1986; Tzvelev, 1989; Watson & Dallwitz, 1992). Recent evidence suggests that grasses had already diversified during the Cretaceous. The evidence came from phytolith analysis (Prasad et al., 2005), tiny crystals of silica formed in the epidermal cells of leaves or floral bracts of grasses and other plants. The discovery of grass phytoliths in coprolites of titanosaurid sauropods that lived in India 65 to 71 million years ago (Prasad et al., 2005), suggested that grasses and dinosaurs coevolved (Piperno & Sues, 2005). Phylogenetic approach to reveal the evolutionary history of grasses in a biogeographical context suggests that Poaceae originated in the African or South American regions of Gondwana during the late Cretaceous (Bouchenak-Khelladi et al., 2010).

Systematic Diversity of the Family Poaceae (Gramineae) in Chile 73

phosphoglycerate, a compound with three carbon atoms. C3 photosynthesis takes place in the leaf mesophyll. C3 grasses are well adapted to temperate climates. In C4 photosynthesis or Hatch-Slack cycle the first detectable metabolic product is oxalacetate, a compound with four carbon atoms. In C4 grasses, C4 activity is confined to the mesophyll and C3 photosynthesis is displaced to the bundle sheath surrounding the vascular tissue (Kranz syndrome). It is presumed that C4 photosynthesis is an adaptation to low CO2 levels and high O2 levels. C4 plants minimize photorespiration sequestering Rubisco in the cells of the bundle sheath making C4 photosynthesis more efficient than C3, especially at high temperatures and arid environments. C4 photosynthesis evolved in four of the 13 subfamilies of Poaceae (Panicoideae, Aristidoideae, Chloridoideae and Micrairoideae). The earliest fossil grass leaves with C4 anatomy is dated 12.5 Ma but Chloridoideae phytoliths have been dated 19 Ma. It has been suggested that C3 photosynthesis is ancestral to the origin of C4 photosynthesis and occurs about 32 Ma during the Oligocene, and that the

The family Poaceae is monophyletic. Characters that unambiguously support the monophyly of the family are the grass-type embryo lateral, peripheral to the endosperm and highly differentiated in the caryopsis, and a *trnT* inversion in the chloroplast genome

The grass family has been divided in a number of subfamilies ranging from two to 13 (for a review see GPWG, 2001). Traditionally, the family was divided in two major groups: Festucoideae (= Pooideae) and Panicoideae (Hitchcock, 1950). The system of grasses (Tzvelev, 1989) also recognized only two subfamilies: Bambusoideae with 14 tribes, and Pooideae, with 27 tribes. In Tzvelev's system, Panicoideae are embedded in Pooideae. One of the most widely used systems is that of Clayton & Renvoize, which divided the family in six subfamilies: Bambusoideae, Pooideae, Centothecoideae, Arundinoideae, Chloridoideae and Panicoideae (Clayton & Renvoize, 1986). The phenetic system of Watson & Dallwitz recognizes seven subfamilies (the same as Clayton & Renvoize + Stipoideae) (Watson & Dallwitz, 1992). The largest proposed number of subfamilies is 13 (Caro, 1982): Bambusoideae, Streptochaetoideae, Anomochlooideae, Olyroideae, Centostecoideae, Oryzoideae, Ehrhartoideae, Phragmitoideae, Festucoideae (= Pooideae), Eragrostoideae (=

The evolutionary history of Poaceae has been deciphered using different molecular markers, such as restriction site maps of the chloroplastidial DNA (Soreng & Davis, 1998), sequences of various chloroplast genes such as *ndhF* (Clark et al., 1995; Sánchez-Ken & Clark, 2010), rpoC2 (Barker et al., 1999), *rbcL* (Barker et al., 1995; Sánchez-Ken & Clark, 2010), matK (Hilu et al., 1999), rps4 (Nadot et al., 1994), and sequences of several nuclear genes such as phytochrome B (Mathews et al., 2000), GBSSI (Mason-Gamer et al., 1998), ITS (Hsiao et al., 1999), and 18S rDNA (Hamby and Zimmer, 1988). The Grass Phylogeny Working Group (GPWG, 2001) combined the data from these sources to produce a phylogeny of the family (Kellogg, 2001). They recognized 12 subfamilies: Anomochloideae, Pharoideae, Puelioideae, Bambusoideae\*1, Ehrhartoideae\*, Pooideae\*, Aristidoideae\*, Arundinoideae\*, Danthonioideae\*, Centothecoideae, Panicoideae\*, and Chloridoideae\*. Three early diverging lineages (Anomochloideae, Pharoideae and Puelioideae) and two major lineages were recognized: a clade comprising the subfamilies Bambusoideae, Ehrhartoideae and Pooideae, called the BEP clade, and the PACCAD clade, containing the subfamilies Panicoideae,

origin of the C4 pathway is polyphyletic (Vincentini et al., 2008).

Chloridoideae), Aristidoideae, Panicoideae and Micrairoideae.

1 An asterisk indicates the subfamilies present in Chile.

(GPWG, 2001).

The economic significance of the grass family is undeniable. Grasses are found on all continents, including Antarctica (e.g. *Deschampsia antarctica*) and are ecologically dominant in some ecosystems such as the African savannas (Kellogg, 2000). Grasslands, in which grasses are the most important floristic component, cover about 40% of the earth surface (Peterson et al., 2010). Most people on Earth depend on grasses, such as wheat, corn, oats, rice, sugarcane, and rye, for a large part of their diet. In addition, domestic animals are fed on diets based largely on forage grasses. Moreover, many of the most serious weeds growing on agricultural land are also members of the grass family.
