Guide to Texas Grasses

4. Classification of the Grasses of Texas

The classification of Texas grasses reflects the subfamilies and tribes presented by the Grass Phylogeny Working Group (2001) and adopted by Barkworth et al. (2003, 2007). The current trend in grass classification has been to increase (e.g., “split”) the number of subfamilies. Historically, 2 subfamilies were recognized, “Panicoid” (Panicoideae) and “Festicoid” (Poöideae). A steady increase in the number of subfamilies since the 1930s has occurred, and currently 16 subfamilies are recognized. The last subfamily added was the Micrairoideae (Barkworth 2007). Within the borders of Texas, 9 of the recognized 16 subfamilies are represented (table 4.1). As throughout North America, 3 subfamilies dominate. Based on the number of species, the Panicoideae (242) is the largest subfamily, followed by the Chloridoideae (213), and the Poöideae (176). These “big three” subfamilies represent 87% of the grass species within the state. Members of the Panicoideae are typically of more mesic habitats and most abundant in Central, South, and East Texas. The Chloridoideae are warm-season grasses characteristic of the more xeric environments and dominate the grass flora in west-central Texas and the Trans-Pecos. Throughout the state, winter and spring annuals are characteristically members of the cool-season Poöideae; cultivated species of this subfamily—Triticum, wheat; Avena, oats; Hordeum, barley; Secale, rye—are most common in the early spring as well. In contrast to the splitting of subfamilies, the number of tribes has been diminishing in number (“lumped”) from the time of Hitchcock’s manuals (1935, 1950). For example, the wellknown Eragrosteae and Chlorideae tribes have been submerged into the Cynodoneae; and the Aveneae is included within the Poeae. Most subfamilies in the state are represented by only 1 or 2 tribes, except the Poöideae, which has 8 (table 4.1). The “big three” subfamilies contain 63% of all the tribes within the state. Gould’s monumental work The Grasses of Texas (1975a) listed 122 genera and 523 species. Hatch, Gandhi, and Brown (1990) reported 131 genera, 545 species, and 60 infraspecific taxa. Jones, Wipff, and Montgomery (1997) increased these numbers significantly (160 genera, 655 species, and 104 infraspecific taxa), primarily by adding ornamentals to the list. This current work lists 181 genera, 723 species, and 189 infraspecific taxa (79 subspecies and 110 varieties). All grass species reported as growing in the state as ornamentals , permanent members of the flora (native or naturalized), or as chance introductions (waifs) have been included. All reported introduced species are included in the checklist. Whether an introduction has become established is uncertain, and all are included here in the off chance that someone might collect one. As previously mentioned, 723 grass species have been reported as occurring in the state and are included in the checklist. There are 668 species keyed with illustrations, short descriptions , and in some cases photographs. There are 6 species included at the end of the species accounts that are late entries. Thus, there are Chapter 4 : CLASSIFICATION OF THE GRASSES OF TEXAS Grasses of Texas 67 49 species (all ornamentals and primarily bamboos ) that are found only in the checklist. There are several reasons for the increase in the number of genera reported for the state. The primary reason is new generic concepts in the Triticeae, Stipeae, and Paniceae. Following are the most recent modifications accepted in this work: 1. Agropyron to Agropyron, Elymus, Leymus, Pascopyrum, Psathrostachys, Pseudoroegneria, Thinopyrum 2. Stipa to Achnatherum, Amelichloa, Hesperostipa, Nassella 3. Panicum to Dichanthelium, Hopia, Phanopyrum, Megathyrsus, Moorochloa, Steinchisma, Urochloa, Zuloagaea The second reason for an increase in the number of genera is that the compiler of this work has a very narrow generic concept, drawing the lines between genera often on 1 or 2 very stable characteristics. Some of the generic “splittings” currently accepted are the following: 1. Agrostis to Agrostis, Lachnagrostis 2. Bouteloua to Bouteloua, Chondrosum 3. Bromus to Anisantha, Bromopsis, Bromus , Ceratochloa 4. Festuca to Festuca, Schedonorus 5. Hordeum to Critesion, Hordeum 6. Phalaris to Phalaris, Phalaroides The addition of a number of species to the list for the state is significant and is primarily the result of increased distributional information contained in the 2 recent volumes (24, 25) of the Flora of North America series. Also, new species concepts based on increased study of certain large and diverse groups (i.e., Dichanthelium , Panicum) have resulted in the recognition of more species and over 60 additional infraspecific taxa. Based on the checklist, 65% of the state’s grass flora are natives, and introduced species account for the...