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Crossidium seriatum

Crum & Steere

Tiny Tassel Moss

G4Apparently Secure Found in 1 roadless area NatureServe Explorer →
G4Apparently SecureGlobal Rank
UnknownThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.122670
Element CodeNBMUS1X070
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryNonvascular Plant
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomPlantae
PhylumBryophyta
ClassBryopsida
OrderPottiales
FamilyPottiaceae
GenusCrossidium
Other Common Names
Petit pompon (FR)
Concept Reference
Anderson, L.E., H.A. Crum, and W.R. Buck. 1990. List of the mosses of North America north of Mexico. The Bryologist 93(4):448-499.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-02-20
Change Date2025-02-20
Edition Date2025-02-20
Edition AuthorsGries, D.; rev. J. Morefield (5/99); rev. R.J. Belland (11/99), rev. A. Tomaino (2009), rev. Soteropoulos (2025)
Threat ImpactUnknown
Range Extent200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Number of Occurrences81 - 300
Rank Reasons
Crossidium seriatum is a wide-ranging perennial moss in semiarid and arid sagebrush steppe, grassland, and desert habitats occurring in western North America from the Yukon Territory and British Columbia, Canada south to Washington, Idaho, Nevada, California, Arizona, and New Mexico, United States and Baja California and Chihuahua, Mexico. European occurrences have been misattributed, and it has also been reported from China. There are over 100 occurrences which face threats from development, conversion to agriculture, road expansion or maintenance, recreational activities, and climate change. It is possible this species is more common than reported due to challenges seeing it during the dry season and its small stature. Little is known about trends, but with a large range extent and large number of occurrences, this species is considered apparently secure.
Range Extent Comments
Crossidium seriatum occurs in western North America from the Yukon Territory and British Columbia, Canada south to Washington, Idaho, Nevada, California, Arizona, and New Mexico, United States and Baja California and Chihuahua, Mexico (FNA 2007, COSEWIC 2014). The type specimen collected from Cedros Island in Baja California, Mexico (Crum and Steere 1958). Reports from Kansas are likely false and based on a poorly preserved juvenile specimen (FNA 2007). While FNA (2007) includes France, Spain, and Switzerland in the distribution, Cano (2004 in Hill et al. 2006) and Hugonnot (2008) state that European plants should be referred to Tortula brevissima. In addition, Crossidium seriatum is reported from China (Tan and Zhao 1997), though the similar Tortula brevissima was documented for China and the comparison to C. seriatum not mentioned (Kou et al. 2015). Range extent was estimated to be almost 2 million square kilometers using herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025 (RARECAT 2024, CBH 2025, GBIF 2025, iNaturalist 2025, NatureServe 2025).
Occurrences Comments
By applying a 1 km separation distance to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are over 100 occurrences rangewide (RARECAT 2024, CBH 2025, GBIF 2025, iNaturalist 2025, NatureServe 2025).
Threat Impact Comments
Though threats are well documented for the northern extent of its range, including residential development and expansion of crops, pasture, and vineyards, road expansion and maintenance, and mountain bike trails, there is insufficient data, including anecdotal accounts, to understand scope and severity of threats for this species (COSEWIC 2014, ECCC 2021, NatureServe 2025). Rangewide, habitats are possibly shifting due to climate change, which "could increase the amount of suitable habitat available (through creating drier conditions in the spring/summer) and also could increase the sporophyte production (through more heavy rainfall events in the fall/winter). Nevertheless, this increased rainfall could also cause more erosion on the silty bluffs where tiny tassel occurs, thereby reducing habitat for the species," so overall impacts of habitat shifting are unknown (ECCC 2021)
Ecology & Habitat

Habitat

This species grows in semiarid and arid regions, and it has been found in sagebrush steppe, grassland, and desert, primarily on mineral, fine or calcareous soils including lacustrine silts (COSEWIC 2014). In Mexico, this species grows on silt at the edge of arroyos at elevations from 300-700 m (Sharp et al. 1994). North of Mexico, this species grows on "sandy soil or rocks, along dry washes, in open or shaded places in deserts" at moderate elevations from 400-600 m (FNA 2007).

Ecology

This species has "physiological traits which allow it to survive in arid and semiarid environments, such as prolonged dormancy, curled leaf margins, leaf papillae and filaments, and leaf hair points" (COSEWIC 2014).

Reproduction

This species produces sporophytes in response to rainfall events, and it is probably capable of regenerating from stem and rhizoid tissue (COSEWIC 2014). It has long-range spore-dispersal by wind currents (ECCC 2021).
Terrestrial Habitats
Shrubland/chaparralGrassland/herbaceousDesertCliff
Other Nations (2)
United StatesN4
ProvinceRankNative
WashingtonSNRYes
NevadaS2Yes
New MexicoSNRYes
ArizonaSNRYes
CaliforniaSNRYes
IdahoSNRYes
CanadaN4
ProvinceRankNative
Yukon TerritoryS1Yes
British ColumbiaS4Yes
Threat Assessments
ThreatScopeSeverityTiming
1 - Residential & commercial developmentUnknownExtreme - seriousHigh (continuing)
2 - Agriculture & aquacultureUnknownExtreme or 71-100% pop. declineHigh (continuing)
2.1 - Annual & perennial non-timber cropsUnknownExtreme or 71-100% pop. declineHigh (continuing)
4 - Transportation & service corridorsUnknownSerious or 31-70% pop. declineHigh (continuing)
4.1 - Roads & railroadsUnknownSerious or 31-70% pop. declineHigh (continuing)
6 - Human intrusions & disturbanceUnknownSerious - moderateHigh (continuing)
6.1 - Recreational activitiesUnknownSerious - moderateHigh (continuing)
11 - Climate change & severe weatherPervasive (71-100%)UnknownHigh (continuing)
11.1 - Habitat shifting & alterationPervasive (71-100%)UnknownHigh (continuing)

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)No
Roadless Areas (1)
California (1)
AreaForestAcres
Sespe - FrazierAngeles National Forest4,254
References (21)
  1. Anderson, L.E., H.A. Crum, and W.R. Buck. 1990. List of the mosses of North America north of Mexico. The Bryologist 93(4):448-499.
  2. Cano, M.J., J. Guerra, and R.M. Ros. 1992. Crossidium seriatum (Pottiaceae, Musci) new to Europe. The Bryologist 95(3):280-283.
  3. Consortium of Bryophyte Herbaria (CBH). 2025. Online. Available: https//:bryophyteportal.org/portal/index.php. (Accessed 2025).
  4. COSEWIC. 2014. COSEWIC assessment and status report on the Tiny Tassel <i>Crossidium seriatum</i> in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. ix + 33 pp.
  5. Crum, H. and W. Steere. 1958. Some bryophytes from Baja California. Southwestern Nauralist 3: 114-123.
  6. Environment and Climate Change Canada (ECCC). 2021. Management Plan for the Tiny Tassel (<i>Crossidium seriatum</i>) in Canada [Proposed]. Species at Risk Act Management Plan Series. Environment and Climate Change Canada, Ottawa. 2 parts, 4 pp. + 17 pp.
  7. Flora of North America Editorial Committee (FNA). 2007b. Flora of North America north of Mexico. Vol. 27. Bryophytes: Mosses, Part 1. Oxford University Press, New York. xxi + 713 pp.
  8. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  9. Hill, M.O., N. Bell, M.A. Bruggeman-Nannenga, M. Brugues, M. J. Cano, J. Enroth, K. I. Flatberg, J.P. Frahm, M. T. Gallego, R. Garilleti, J. Guerra, L. Hedenas, D. T. Holyoak, J. Hyvonen, M. S. Ignatov, F. Lara, V. Mazimpaka, J. Munoz and L. Soderstrom. 2006. An annotated checklist of the mosses of Europe and Macaronesia. Journal of Bryology 28: 198-267.
  10. Hong, W.S. 1992. Plagiochila in western North America. The Bryologist 95(2):142-147.
  11. Hugonnot, V. 2008. <i>Crossidium seriatum</i> Crum & Steere excluded from the bryoflora of France, new locality of <i>Tortula brevissima</i> Schiffn. in Finistère. Bulletin de la société botanique du Centre-Ouest: 563-564.
  12. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  13. Kou, J., Song, S.S., Feng, C., Bai, X.L., Yu, C.Q. and X.M. Shao. 2015. A new species record of <i>Tortula</i> and range extension of one species of <i>Grimmia</i> in China. Cryptogamie, Bryologie 36(3): 235-241.
  14. McIntosh, T.T. 1989. Bryophyte records from the semiarid steppe of northwestern North America, including four species new to North America. The Bryologist 92(3):356-362.
  15. Morefield, J.D., editor. 2001. Nevada rare plant atlas [with rare plant fact sheets]. Available as a pdf file at: http://heritage.nv.gov/atlas/atlas.html. Compiled by the Nevada Natural Heritage Program, Carson City, for the U.S. Fish and Wildlife Service, Reno, Nevada.
  16. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  17. NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2024. Version: 1.1.1 (released Oct 01, 2024).
  18. Sharp, Aaron J. et al. 1994. The Moss Flora of Mexico. Buck, William R., Thomas Wm. Wayt, Daniel F. Thomas, editors.
  19. Stark, L. R. 1999. Five globally rare species of mosses from southern Nevada: An update on their distribution ranges, including recent unpublished findings from predominantly gypsum/sandstone habitats in the Lake Mead National Recreation Area and associated Bureau of Land Management lands. Las Vegas: University of Nevada, unpublished report. 11 pp.
  20. Stark, L.R., and A.T. Whittemore. 1992. Additions to the bryoflora of southern California. The Bryologist 95(1):65-67.
  21. Tan, B.C., and J.C. Zhao. 1997. New Moss records and range extensions of some xeric and alpine moss species in China. Cryptogamie. Bryologie, lichénologie 18(3): 207-212.