• Corpus ID: 182409931

Ajo Peak to Tinajas Altas: A flora of southwestern Arizona. Part 6. Poaceae – grass family

@inproceedings{Felger2014AjoPT,
  title={Ajo Peak to Tinajas Altas: A flora of southwestern Arizona. Part 6. Poaceae – grass family},
  author={Richard Stephen Felger and Sue Rutman and Jim Malusa},
  year={2014}
}

• R. Felger, S. Rutman, J. Malusa
• Published 2014
• Geography

A floristic account is provided for the grass family as part of the vascular plant flora of the contiguous protected areas of Organ Pipe Cactus National Monument, Cabeza Prieta National Wildlife Refuge, and the Tinajas Altas Region in southwestern Arizona. This is the second largest family in the flora area after Asteraceae. A total of 97 taxa in 46 genera of grasses are included in this publication, which includes ones established and reproducing in the modern flora (86 taxa in 43 genera), some occurring at the margins of the flora area or no long known from the area, and ice age fossils. At least 28 taxa are known by fossils recovered from packrat middens, five of which have not been found in the modern flora: little barley (Hordeum pusillum), cliff muhly (Muhlenbergia polycaulis), Paspalum sp., mutton bluegrass (Poa fendleriana), and bulb panic grass (Zuloagaea bulbosa). Non-native grasses are represented by 27 species, or 28% of the modern grass flora. No other large family in the region has such a high percentage of non-natives. Buffelgrass (Cenchrus ciliaris), fountain grass (Cenchrus setaceum), and Schismus spp. are invasive species of major concern. The most diverse grass genera in the flora are Muhlenbergia (10 species), Bouteloua (6 species), and Aristida, Eragrostis, Panicum, and Sporobolus (4 species each). Eragrostis pectinacea var. miserrima is treated as a synonym of E. pectinacea var. pectinacea and Muhlenbergia alopecuroides (Lycurus setosus) as a synonym of Muhlenbergia phleoides (Lycurus phleoides). The modern, established grass flora includes 49 perennials and 37 annuals or ephemerals, of which 20 are summer or hot-season taxa, 12 winter-spring or cool-season taxa, and 5 are non-seasonal. This floristic treatment includes brief descriptions, illustrations, identification keys, common names (when available in English, Spanish, and the local O’odham language), local and global distributions, fossil records from packrat middens, and specimen citations. POACEAE – Grass Family This publication is an account of the grasses as part of the vascular plant flora of the contiguous protected areas of Organ Pipe Cactus National Monument, Cabeza Prieta National Wildlife Refuge, and the Tinajas Altas Region in southwestern Arizona (Fig. 1). This is the sixth Felger, Rutman, and Malusa: Flora of SW Arizona, Poaceae 2 contribution to our flora, published in a series in Phytoneuron and also posted open access on the website of the University of Arizona Herbarium (ARIZ). The first article in this series includes maps and brief descriptions of the physical, biological, ecological, floristic, and deep history of the flora area (Felger et al. 2013a). This flora includes the modern, present-day taxa as well as fossil records from packrat middens. Explanation of the format for the flora is provided in part 3 (Felger et al. 2013c). Figure 1. Flora area in southwestern Arizona. Map prepared by Ami Pate of Organ Pipe Cactus NM, 2013. The following generalized descriptions include the grasses in the flora area and not necessarily the same grasses in other regions. There are many variations and not all can be covered in this brief description. Annual/ephemeral and perennial herbs and some reedor bamboo-like (Phragmites). Roots fibrous; rhizomes and stolons sometimes present. Culms hollow between the nodes and solid at nodes, or less often also solid between the nodes. Leaves basal or cauline (on the culm), 2-ranked, consisting of the sheath, ligule, and blade. Leaf sheaths are partially to fully enclosing the stem, and either open (margins overlapping, not fused) or closed (margins fused). Junction of the leaf sheath and blade called the collar, usually with a ligule, often a scale-like or hairy extension at the top of the leaf sheath and blade and facing the culm (membranous throughout, membranous at the base and topped by cilia, or entirely of hairs). Leaf blades linear with parallel veins, flat or variously folded or inrolled (involute). Felger, Rutman, and Malusa: Flora of SW Arizona, Poaceae 3 In grasses there are several kinds of stems, including culms, rhizomes, and stolons. Technically, “stem” is a general term that can be applied to all of these. The aerial stem of a grass is termed a culm. Inflorescences generally are terminal, sometimes on lateral branches from the culm. (Measurements for culms therefore do not include inflorescences.) Flowers small, bisexual, or unisexual and the plants monoecious or dioecious. Flowers in spikelets. Terminology for grass inflorescences treats the spikelet as the basic unit in the way the flower is treated in general terminology for flowering plants. Spikelets are in spikes, panicles, or rarely racemes. Panicle branches may be racemose (spikelets with pedicels), spicate (spikelets sessile), or rames (spikelets in pairs, one sessile, one pedicellate), or unilateral (spikelets all on one side of the branch) or not. Spikelets of bracts and 1 or more florets, the bracts and floret(s) 2-ranked (alternate on opposite sides of the rachilla). Bracts variously awned or not; lowermost bracts (glumes) paired or sometimes reduced to 1. The floret includes 2 bracts, the lemma below and the palea above, these enclosing the actual flower (the palea sometimes reduced or absent). In spikelets of more than one floret the lowermost or uppermost floret or florets sometimes staminate or reduced and sterile. Perianth segments (lodicules) of greatly reduced scales, mostly 2 (3 in Aristida and Pappostipa), often swelling and spreading the floret open at anthesis, or sometimes absent. Pistil single, superior (of 3 united carpels, but functionally with 1 carpel containing 1 ovule). Stamens usually 3, sometimes 1 or 2. Stigmas generally 2 and feathery (plumose). Fruits of specialized achenes (1-seeded) called a caryopsis (caryopses, plural), where the seed is fused to the fruit wall (pericarp), or an actual achene in which the seed separates from the pericarp (Dactyloctenium and Sporobolus). The caryopsis (including the tightly enclosing fertile lemma and palea in panicoids) or the achene is conveniently referred to as the “grain.” Some grasses, including species of Bromus, Festuca, and Sporobolus, produce mostly or only cleistogamous florets. These are florets that remain closed and produce seeds without exposing the stamens and stigmas and thus are self-fertilized. Cleistogamous grasses tend to occur in dry areas with erratic rainfall, sparse vegetation, and lighter soils (Lord 1981). Five grasses in the flora area produce cleistogenes at the stem bases or in leaf axils: Cottea pappophoroides, Disakisperma dubium, Enneapogon desvauxii, Muhlenbergia appressa, and M. microsperma. The cleistogenes are modified cleistogamous inflorescences or spikelets, lacking glumes and awns, and the grain is typically larger (heavier) than the grain from “normal” (chasmogamous) florets. Cleistogenes provide a reproductive strategy in addition to that of the usual terminal (chasmogamous) inflorescences, such as when those inflorescences are lost to herbivores or do not develop due to drought. Grasses in the flora area are distributed among six subfamilies following the classification in Soreng et al. (2013) and the Grass Phylogeny Working Group (2012): Subfamily Aristidoideae: Aristida Subfamily Arundinoideae: Phragmites Subfamily Danthonioideae: Schismus Subfamily Chloridoideae: Tribe Eragrostideae: Subtribe Cotteinae: Cottea, Enneapogon Subtribe Eragrostidinae: Eragrostis Tribe Zoysieae: Subtribe Sporobolinae: Sporobolus Tribe Chlorideae: unplaced genus: Dactyloctenium Subtribe Boutelouinae: Bouteloua Felger, Rutman, and Malusa: Flora of SW Arizona, Poaceae 4 Subtribe Eleusininae: Chloris, Cynodon, Dinebra, Diplachne, Disakisperma, Leptochloa Subtribe Hilariinae: Hilaria Subtribe Gouiniinae: Tridentopsis Subtribe Monanthochloinae: Distichlis Subtribe Muhlenbergiinae: Muhlenbergia Subtribe Pappophorinae: Pappophorum Subtribe Scleropogoninae: Dasyochloa Subfamily Panicoideae Tribe Paniceae Subtribe Anthephorinae: Digitaria Subtribe Boivinellinae: Echinochloa Subtribe Cenchrinae: Cenchrus, Setaria, Zuloagaea Subtribe Melinidinae: Eriochloa, Urochloa Subtribe Panicinae: Panicum Tribe Paspaleae: Hopia, Paspalum Tribe Sacchareae Subtribe Anthistiriinae: Heteropogon Subtribe Sorghinae: Bothriochloa, Sorghum Subtribe Tripsacinae: Zea Subfamily Pooideae Tribe Bromeae: Bromus Tribe Hordeeae Subtribe Hordeinae: Elymus, Hordeum Subtribe Triticinae: Triticum Tribe Meliceae: Melica Tribe Poeae Subtribe Agrostidinae: Polypogon Subtribe Aveninae: Avena Subtribe Poinae: Poa Subtribe Loliinae: Festuca Subtribe Phalaridinae: Phalaris Tribe Stipeae: Pappostipa Spikelets in the subfamily Panicoideae are generally paired (sometimes in triplets on terminal branchlets), the members of a unit usually with pedicels of different lengths or one spikelet sessile, or reduced, or sometimes absent. The individual spikelets detach below the glumes and have 2 florets, the lower one staminate or sterile, often reduced to just a lemma, the upper floret usually bisexual. Many other grasses have spikelets with 2 florets, but rarely have the lower floret staminate or sterile and the upper one bisexual. Two major kinds of spikelets are notable among the subfamily Panicoideae, the andropogonoid and the panicoid spikelets. Andropogonoid spikelets are seen in Bothriochloa, Heteropogon, and Sorghum in the tribe Sacchareae. There is a basic pattern, but a daunting array of variation. The spikelets are in pairs (triplets often at branch tips—the descriptions that follow are for the paired spikelets). The pairs have 1 sessile/subsessile spikelet and 1 stalked (pedicelled) spikelet. Among those in the flora area the pedicelled spikelet is smaller than the sessile/subsessile one or reduced or absent. The sessile/subsessile spikelet has a staminate or sterile (reduced) floret below and a bisexual or pistillate floret above. The spikelet pair or unit falls with its