The Genera of Chloridoideae (Gramineae)

The Genera of Chloridoideae (Gramineae)

in the Southeastern United States1,2

Gordon C. Tucker3

1Prepared for the Generic Flora of the Southeastern United States, a long-term project made possible by grants from the National Science Foundation and at this writing supported by BSR- xxxxx (Norton G. Miller, principal investigator), under which preparation of this account was commenced, and BSR- xxxxxx (Walter Judd, principal investigator). This treatment, the umpteenth in the series, follows the format established in the first paper (Jour. Arnold Arb. 39: 296-346. 1958) and continued to the present. The area covered by the Generic Flora includes North and South Carolina, Georgia, Florida, Tennessee, Alabama, Mississippi, Arkansas, and Louisiana. The descriptions are based primarily on the plants of this area, with information about extraregional members of a family, subfamily, or genus in brackets [ ].

Norton Miller, Carroll Wood, Ken Robertson, Tom Rosatti, Gerrit Davidse, John Ebinger, Dave Seigler, Ihsan AlShehbaz, Wilma Campbell, and Barbara Nimblett have provided suggestions, encouragement, and technical assistance and I wish to thank them for making my work on the Generic Flora enjoyable and rewarding. William J. Crins has shared his extensive familiarity with grasses, particularly of Muhlenbergia and Eragrostis. Thanks are extended to the staffs of the New York State Library, the Botany Libraries of Harvard University, Missouri Botanical Garden Library, Booth Library of Eastern Illinois University, and the Illinois Natural History Survey Library for providing access to many references. I thank the curators of the following herbaria who have sent specimens or provided hospitality and access to the collections under their care during my visits: A, CLEMS, CONN, ECON, EIU, GH, ILL, ILLS, IND, ISM, MO, MU, MUHW, NEBC, NY, NYS, SIU, and WIS.

The illustrations used here were published earlier as Figures x-x in Christopher Campbell's account of the subfamilies and tribes of grasses prepared for the Generic Flora (see Footnote 2 below). The figures were drawn by Karen Stoutsenberger during a previous grant period (NSF BMS-21469, Carroll Wood, principal investigator) under the supervision of Carroll Wood, Kenneth R. Robertson, and Christopher Campbell, who also prepared the materials.

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2For an account of the family, see C. S. Campbell, The subfamilies and tribes of the Gramineae (Poaceae) in the southeastern United States. Jour. Arnold Arb. 66: 123-199. 1985.

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3Stover-Ebinger Herbarium, Department of Biological Sciences, EasternIllinoisUniversity, Charleston, Illinois61920; e-mail:

Chloridoideae Rouy, Fl. France 14: 2. 1913.*

Chloridoideae Kunth ex Beilschm. {{fide FNA 23}}

Perennials or annuals of diverse habitats. Roots fibrous; rhizomes often present. Microhairs short and stout; anatomy kranz (PS type), the photosynthetic pathway exclusively C4 (except one Eragrostis sp.). Stems erect or decumbent, simple or sometimes branched near base, sometimes rooting at the nodes, the internodes hollow. Leaves cauline or basal, few or many, not distinctly distichous (distinctly distichous in Distichlis and Monanthochloë); sheath open, longer or shorter than the corresponding internode; ligule membranaceous; blade linear or lanceolate, not auriculate, flat, convolute, or involute [terete]. Inflorescence a panicle, spike, raceme, or group of racemes, often secund, often partly included in the subtending sheath. Spikelets laterally compressed, 1-15 (30) flowered; glumes 2, typically equal, about as long as the first lemma; rachilla articulated above (infrequently below) glumes; flowers bisexual (unisexual, the plants dioecious in Distichlis, Monanthochloe,and some Eragrostis); lemmas oblong to lanceolate, 1-3 nerved; paleas elliptic, mostly about as long as the lemmas, usually 2-nerved. Lodicules 2, cuneate or truncate (less often rounded or acuminate), fleshy. Stamens 3 (infrequently 1 or 2); anthers ellipsoid to linear. Ovaries ellipsoid to oblong, glabrous or hairy apically; styles 2 [3 in Munroa], separate, long, short, or obsolete, stigmas terminal,plumose. Fruit a caryopsis (achene with free pericarp in a few genera), subterete to cylindric, sometimes flattened laterally, linear, oblong, or ellipsoid; hilum punctiform to linear, from 1/5 to nearly as long as grain; embryo large, typically 1/3 –3/4 the length of the grain; endosperm solid. Base chromosome number 10 (7, 8, 9, 12 in one or more genera). (Eragrostoideae Pilger, Nat.Pfl. ed. 2, 14d: 167. 1956*) Type genus: Chloris Sw.

A large subfamily, worldwide in temperate and tropical regions. The hallmark of the Chloridoideae is the typically three-nerved lemma, consistently kranz anatomy, and distinctive microhairs. There is some similarity to the Arundinoideae. The Chlorodoideae is one of the three largest subfamilies of the grasses, along with the Pooideae and Panicoideae. The subfamily in its present sense was first proposed by Pilger (1954).

Five tribes were recognized by Clayton and Renvoize. The Eragrostideae Stapf (76 genera) and the Cynodonteae Dumort. (58 genera) are both large and widely distributed. In contrast, the Pappophoreae Kunth (five genera), Leptureae Holmberg (monotypic) and Orcuttiae Reeder (three genera) are quite small.

All genera of the Chloridoideae have the C4 photosynthetic pathway, the only exception being Eragrostiswalteri, which most likely is a case of reversion (Chapman). Three of the eight recognized variants of C4 occur in the subfamily. The “Classical NAD-ME” type has centripetally arranged chloroplasts in the bundle sheath cells, the decarboxylating enzyme is NAD malate dehydrogenase; this type occurs in Buchloë, Cynodon, and some species of Leptochloa. The “Classical PCK” type has centrifugal or uneven arrangement of the chloroplasts, and the decarboxylating enzyme is phosphoenolpyruvate carboxykinase; this occurs in Chloris, Dactyloctenium, Spartina, Zoysia, and some Leptochloa. The third type, the “Triodia type”, has centrifugally arranged chloroplasts, and NAD malate dehydrogenase as the decarboxylating enzyme. This type occurs in several Australian genera, including Triodia and Monodia, but not in any genera native or naturalized in our area.

Molecular systematics and integrity of subfamily have received some attention. A monophyletic origin for the subtribe Muhlenbergiinae is supported by restriction site analysis of chloroplast DNA. Duvall et al. investigated of 25 species of Eragrostideae, one species of Cynodonteae (Eustachysdistichophylla), and one species of Pooideae. They detected 124 restriction sites, of which 67 were variably present and shared by two or more species. Cladistic analyses established that members of the Muhlenbergiinae, including the genera Muhlenbergia, Blepharoneuron, Bealia, Chaboissaea, Lycurus and Pereilema, share seven restriction site mutations and are strongly supported by the data as a monophyletic subtribe. The monotypic Great Plains genus Redfieldia also clustered with the subtribe Muhlenbergiinae in their analysis, perhaps indicative of a past intergeneric hybridization event or convergent evolution. Their restriction site data also weakly support a relationship (six shared mutations) between Erioneuron, Munroa, and Dasyochloa.

The reed-like genus Neyraudia, previously included in the Arundinoideae and treated in the GFSEUS account of that subfamily, is now generally placed in the Chloridoideae. It appears to be most closely related to …. (Barkworth Grass Manual).

------Biogeography; 17 genera in the Intermountain West

In several genera, the mature pericarp is more or less free from the seed, being fused to the seed only in the vicinity of the hilum. For such fruits, the term achene has been used. Also the terms modified caryopsis and cistoid pericarp have been proposed, though scarcely taken up. In Crypsis, Eleusine, and Sporobolus, for example, the mesocarp and endocarp disintegrate during development and maturation leaving only the exocarp. When moistened, the seed may actually be extruded from the mature pericarp (Sendulsky et al.).

Reproductive biology of the subfamily is distinct. In 13 genera, cleistogamous spikelets have been reported noted in one or more species, including only Leptochloa and Muhlenbergia in the southeast (Connor). Cleistogamous subterranean spikelets are known from only four genera of the family; one of the representatives is a species of Chloris. Gynomonoecy is known from only one genus, Munroa (Connor, 1981), which is apparently also self-incompatible. Blepharidachne has three monoecious species, and the fourth, B. kingii, has bisexual flowers (Connor). Stamens number 1, 2, or 3, depending on the species (Anton & Hunziker). The Chlorideae have a high number of dioecious genera, seven (Bouteloa, Buchloë, Buchlomimus, Cyclostachya, Opizia, Pringleochloa, Soderstromia), more than any other tribe in the family, while in the Eragrostideae only Neeragrostis and Scleropogon are dioecious (Connor). Apomixis is documented from three genera of the Chloridoideae (Bouteloua, Chloris, Eragrostis).

References:

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----- & -----. Competition and facilitation in marsh plants. Am. Nat. 142: 718-724. 1993. [Spartina patens, Distichlis spicata in California.]

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Ernst, W.H.O., & D.J. Tolsma. Dormancy and germination of semi-arid annual plant species, Tragusberteronianus and Tribulus terrestris. Flora : Morphologie, Geobotanik, Okologie 181(3/4): 243-251. 1988. [Tragus sp.]

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Ernst, W.H.O., J.W.M. van de. Staaij, & H.J.M. Nelissen. Reaction of savanna plants from Botswana on UV-B radiation. Plant ecology 128(1/2): 162-170. 1997. [Chloris virgata, Tragusberteronianus.]