Sporobolus silveanus Swallen:
United States (North America)

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Sporobolus silveanus occurs primarily in the eastern fifth of Texas and small portions of adjacent southwestern Louisiana and southeastern Oklahoma. The distribution map in Weakley and Peterson (1998) indicates that Sporobolus silveanus is found primarily in the pine forest and oak woodland belts of southeast Texas and adjacent Louisiana, but it also indicates seemingly isolated records from prairie regions of northeast Texas and southeast Oklahoma, where the species is locally abundant in some prairie remnants. Sporobolus silveanus may be overlooked by general collectors, and it is likely that its distribution is (or historically was) more continuous across its range than the current information suggests.

In Texas, occurrence of this species is documented from Angelina, Brazos, Galveston, Hardin, Harris, Jasper, Lamar, Newton, Orange, Rains, Tyler and Van Zandt counties (Texas BCD, 1999); information about known occurrences in Franklin County (Daphne Prairie) and Hunt County (Clymer Meadow and other remnants) has not yet been developed (Jim Eidson, pers. comm., 1999). In Louisiana it has been collected from Allen and Calcasieu parishes (Thomas and Allen, 1993). In Oklahoma it is known from Jeter Prairie in Bryan County (Jim Eidson, pers. comm., 1999).

Perennials, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems erect or ascending, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stem intern odes hollow, Stems with inflorescence less than 1 m tall, Stems with inflorescence 1-2 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Leaf blades glaucous, blue-green, or grey, or with white glands, Ligule present, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence branches more than 10 to numerous, Flowers bisexual, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikele ts solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes 1 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma similar in texture to glumes, Lemma 1 nerved, Lemma glabrous, Lemma apex acute or acuminate, Lemma awnless, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea about equal to lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Isotype for Sporobolus silveanus Swallen
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Card file verified by examination of alleged type specimen
Preparation: Pressed specimen
Collector(s): W. Silveus
Year Collected: 1940
Locality: US 90, 10 mi NE of Orange., Orange, Texas, United States, North America

Holotype for Sporobolus silveanus Swallen
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Card file verified by examination of alleged type specimen
Preparation: Pressed specimen
Collector(s): W. Silveus
Year Collected: 1940
Locality: US 90, 10 mi NE of Orange., Orange, Texas, United States, North America

Isotype for Sporobolus silveanus Swallen
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Card file verified by examination of alleged type specimen
Preparation: Pressed specimen
Collector(s): W. Silveus
Year Collected: 1940
Locality: US 90, 10 mi NE of Orange., Orange, Texas, United States, North America

Comments: In southeast Texas and adjacent Louisiana, Sporobolus silveanus occurs primarily in pine woodlands or forests on sandy substrates, as well as adjacent glades and pine-oak barrens (Weakley and Peterson, 1998). In northeast Texas and adjacent southeastern Oklahoma, Sporobolus silveanus is a locally common component of prairie grasslands on Alfisol soils. In some cases, these Alfisols occur as small inclusions within a matrix of heavier Vertisol soils. In Franklin County, Texas it occurs on pimple (mima) mounds (Jim Eidson, pers comm., 1999.)

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: Although it occurs in both forest and prairie situations in portions of three states, Sporobolus silveanus is seldom collected. The species is locally abundant however on some prairie remnants, perhaps those where late-season haying favors this species over Schizachyrium scoparium, Panicum virgatum and other perennials that might dominate under mid-season mowing regimes (Jim Eidson, pers. comm., 1999). Sporobolus silveanus might be routinely overlooked, or in many sites it might be suppressed and difficult to detect.

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Sporobolus silveanus is a moderately widespread perennial grass endemic to forests and prairies of eastern Texas, western Louisiana and extreme southern Oklahoma. It has not been the target of directed field research, and its global abundance can only be estimated. It is seldom collected; the limited current information suggests fewer than 100 occurrences globally. Whether this estimate reflects reality or is simply the result of insufficient information and lack of survey effort remains to be determined.

Comments: Threats to Sporobolus silveanus have not been demonstrated but are thought to include fire suppression in both forest and prairie habitat; haying or mowing at seasons that favor the increase of other mid-height and tall grasses; and broader, general threats such as conversion of native prairie to agricultural field or improved pasture, or the conversion of mixed forest to pine plantation. Suburban development is a general threat in some of the north Texas range.