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Tall Dropseed - Sporobolus compositus
Other Names:
Sporobolus asper
State Rank Reason (see State Rank above)
DRAFT: Requesting feedback on the 2026 revised rank, factors, and State Rank Reason outlined below and in the Conservation Status Rank Report.
Sporobolus compositus is rare in eastern Montana. In the last few years, approximately 2 dozen observations of the species have been documented, greatly increasing the known distribution and abundance of the species in the state. Population levels appear to be relatively small, and the total statewide populations are likely in the low thousands. The species appears to tolerate or respond favorably to some disturbance and several occurrences are along roads, where favorable habitats may have been created. Due to the relatively small population levels, the species may still be vulnerable in the state. Surveys in potentially suitable habitat may locate additional occurrences. These surveys, in conjunction with more comprehensive data on existing occurrences, including data on population sizes and extent, on habitat quality, and potential threats, if any, may show that the species is not vulnerable to extirpation in the state.
General Description
Perennial. Stems 30–80 cm. Leaves: blades 2–4 mm wide; throat with a tuft of hairs. Inflorescence a contracted panicle 5–15 cm long, mostly enclosed in leaf sheath. Spikelets 4–6 mm long. Lemmas 3–6 mm long (Lavin in
Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Phenology
Mature fruit in August.
Diagnostic Characteristics
Tall Dropseed -
Sporobolus compositus, SOC
*Habit: Perennial.
*Panicle: Contracted (appressed), but much longer than wide
and usually partially enclosed in the leaf sheath.
*Stem: Base is erect.
*Spikelets: 3 mm or more long. Both glumes are not as long or longer than the lemma.
Alkali Dropseed -
Sporobolus airoides*Habit: Perennial.
*Panicle: Diffuse, greater than 4 centimeters long, and about as long as wide
and usually fully exerted from the leaf sheath.
*Stem: Base is decumbent.
*Spikelets: 2-2.5 mm long.
Sand Dropseed -
Sporobolus cryptandrus*Habit: Perennial.
*Panicle: Contracted (appressed), greater than 4 centimeters long, and much longer than wide
and enclosed in an arcuate leaf sheath.
*Stem: Base is erect.
*Spikelets: 2.5 mm or shorter. Both glumes are not as long or longer than the lemma.
Small Dropseed -
Sporobolus neglectus, SOC
*Habit: Annual.
*Panicle: Contracted (narrow), less than 4 cm long,
and usually partially enclosed by the leaf sheath.
*Spikelets: 2-3 mm long.
Prairie Dropseed -
Sporobolus heterolepis, not documented in Montana
*Habit: Perennial.
*Panicle: Open, greater than 4 centimeters long, and much longer than wide
and usually entirely exerted from the leaf sheath.
*Spikelets: At least one of the glumes is as long or longer than the lemma.
Species Range
Montana Range
Range Descriptions
Native
Range Comments
Collected in Carter County; sporadic throughout most of North America (Lavin in Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Observations in Montana Natural Heritage Program Database
Number of Observations: 29
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
Relative Density
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
Open forests and grasslands on the plains.
National Vegetation Classification System Groups Associated with this Species
Wetland and Riparian
Alkaline - Saline Wetlands
Wet Meadow and Marsh
Stewardship Responsibility
Threats or Limiting Factors
STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).
References
- Literature Cited AboveLegend:
View Online Publication- Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
MTNHP Threat Assessment. 2021. State Threat Score Assignment and Assessment of Reported Threats from 2006 to 2021 for State-listed Vascular Plants. Botany Program, Montana Natural Heritage Program, Helena, Montana.
- Additional ReferencesLegend: View Online Publication
Do you know of a citation we're missing?- Brey, C.W. 1998. Epidemiology of wheat curl mite (Aceria tosichella K.) and wheat streak mosaic virus on feral grass species and effect of glyphosate on wheat curl mite dispersal. Ph.D. Dissertation. Bozeman, MT: Montana State University. 136 p.
- Flora of North America Editorial Committee. 2003. Flora of North America North of Mexico. Vol. 25. Magnoliophyta: Commelinidae (in part): Poaceae, part 2. Oxford Univ. Press, New York. xxv + 781 pp.
- Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
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