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INTRODUCTORY

SPECIES: Dodecahema leptoceras
AUTHORSHIP AND CITATION:
Sclafani, Christie J. 2013. Dodecahema leptoceras. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/forb/dodlep/all.html [].

FEIS ABBREVIATION:
DODLEP

COMMON NAMES:
slenderhorn spineflower
slender-horned spineflower

Photo by Anuja Parikh and Nathan Gale.

TAXONOMY:
The scientific name of slenderhorn spineflower is Dodecahema leptoceras (A. Gray) Reveal & Hardham (Polygonaceae). Slenderhorn spineflower is the only recognized species within its genus [2,14,16].

SYNONYMS:
Centrostegia leptoceras (A. Gray ex Benth.)
Chorizanthe leptoceras (A. Gray ex Benth.) S. Wats. [12]
Eriogonella leptoceras (A. Gray) Goodman [9]

LIFE FORM:
Forb
INFORMATION AVAILABLE:
In November of 2012 an extensive search was done to locate information on slenderhorn spineflower (see FEIS's list of source literature), with few results. The following paragraphs provide details of the available information.

DISTRIBUTION AND OCCURRENCE

SPECIES: Dodecahema leptoceras
GENERAL DISTRIBUTION:
Slenderhorn spineflower is endemic to the Transverse and Peninsular ranges of southern California. As of 2010, it was known from 20 populations in Los Angeles, San Bernardino and Riverside counties [4,19]. The US Fish and Wildlife Service [19] provides details on slenderhorn spineflower population occurrences.

Distribution of slenderhorn spineflower. Map courtesy of the Jepson Herbarium [17].

States [18]:
CA

SITE CHARACTERISTICS:
Slenderhorn spineflower is associated with intermediate to late successional stages [7] in alluvial scrub habitats [8]. It typically occurs in washes, on flat benches and terraces away from active stream channels [8], and in uplands or dry drainage channels not associated with developed floodplains [7]. Textures on soils supporting slenderhorn spineflower include silt [1], loamy sand [23], and sand [7,14,23]. These soils may contain gravel or cobble [1,14]. Studies on the geomorphology of alluvial scrub habitats revealed the soil sediments where slenderhorn spineflower grows are 100+ years old [23].

Slenderhorn spineflower grows at elevations from 656 to 2,296 feet (200-700 m) [4,7,19]. Surveys of 8 slenderhorn spineflower populations found the species was most common on slightly acid (pH 6.4) silts with low levels of nitrogen, phosphorus, and organic matter and low electrical conductivity and “fairly low” cation exchange [1].

PLANT COMMUNITIES:
Slenderhorn spineflower occurs in various vegetation types. Surveys on 8 sites found no indicator species that consistently cooccurred with slenderhorn spineflower [1], although California broomsedge (Lepidospartum squamatum) is considered an indicator for alluvial scrub habitats in general [19]. Slenderhorn spineflower is apparently not restricted by vegetation type; its habitats are characterized by edaphic factors [1,6].

Photo by Anuja Parikh and Nathan Gale.

Slenderhorn spineflower is noted in grasslands dominated by nonnative annuals; in coastal sage scrub [1,7], chamise (Adenostoma fasciculatum), and other chaparral [1,7], and in woodlands dominated by coast live oak (Quercus agrifolia) [1], western sycamore (Platanus racemosa), California juniper (Juniperus californica), and Fremont cottonwood (Populus fremontii) [1,19].

Slenderhorn spineflower is sometimes found on soil crusts with lichens and mosses [1,19]; however, some slenderhorn spineflower habitats have little to no soil crust cover [1]. In western Riverside and San Bernardino counties, percent soil crust cover was negatively correlated with the number of involucres/slenderhorn spineflower plant (r = -0.49, P=0.03), while percent annual grass or forb cover was not significantly correlated with slenderhorn spineflower presence [6].

See the Fire Regime Table for a list of plant communities in which slenderhorn spineflower may occur and information on the fire regimes associated with those communities.

GENERAL INFORMATION ON BIOLOGY AND ECOLOGY, FIRE, AND MANAGEMENT

SPECIES: Dodecahema leptoceras
BIOLOGY AND ECOLOGY:
Botanical description::
Slenderhorn spineflower is a small annual plant arising from a shallow, slender taproot [1,14]. It forms a basal rosette that sometimes persists after flowering [6]. The leaves are narrowly oblanceolate, ranging from 1.2 to 3.1 inches (3-8 cm) in diameter and becoming red at maturity. The branched flowering stalk is 1.2 to 4 inches (3-10 cm) tall with flower clusters [2]. Each of the 6 involucres at the base of a flower cluster has an awn at its base and apex; this distinguishes slenderhorn spineflower from other spineflower species (Chorizanthe and Systenotheca spp.) [14]. Each white to pink flower produces a single achene [2].

Photo by Aaron Schusteff.

Raunkiaer [13] life form:
Therophyte

Seasonal development:
Slenderhorn spineflower germination occurs from late February to late May, usually after winter or spring rains [5,6]. Some germination and establishment continues throughout summer [6]. Flowering occurs from May to June [4]. Ferguson and others [6] observed that during that time, slenderhorn spineflower had “the largest floral displays” of all flowering species present in alluvial scrub habitats. The flower clusters are indeterminate, continuing to grow and bloom until plant death. Plants germinating late in the growing season skip the rosette stage, producing flowering stems directly from the root crown [6].

Regeneration:
Mating system: Populations are apparently highly diverse genetically. Genetic and field studies suggest that slenderhorn spineflower is mostly outcrossing, with some self-pollination. The mating system is “highly” protandrous. Because some plants display flowers in male and female phases at the same time, some selfing is possible. Laboratory studies found little evidence of either inbreeding or low genetic diversity despite small population sizes. The authors concluded that levels of genetic diversity for slenderhorn spineflower “are high for plants in general and remarkable for both endemic, highly restricted plant taxa and annual taxa” [6].

Field studies show evidence of insect pollination. Both ants and flying insects were observed visiting slenderhorn spineflower flowers, although a wasp (Plenoculus davisii) was the only species observed actually pollinating flowers [6].

Establishment: As an annual, slenderhorn spineflower establishes solely from seed. It produces 3 to 507 seeds/plant [5]. Small spines and hooks on the involucres likely aid animal dispersal of the seeds. The achenes have no mechanisms for dispersal, but since slenderhorn spineflower occurs on alluvial soils, sheet flows during heavy rains may disperse the achenes [19].

Seeds are stored in the soil seed bank. Seed viability was unknown as of 2012, although seeds stored in the soil seed bank are likely long-lived [5]. Ferguson and others [6] speculated that in a given year, recruitment may result from seeds stored across several years and recommended prioritizing research on seed bank dynamics of slenderhorn spineflower.

Current-year precipitation is critical in determining slenderhorn spineflower’s rate of establishment and seed production. In a year with steady summer rains in western Riverside and San Bernardino counties, many hand-marked slenderhorn spineflowers favored vegetative over reproductive growth. The next year, which was drier, marked plants dried out with summer heat. However, at the next rainstorm, plants appeared in the same locations as the marked, dried-out plants measured earlier. The authors interpreted this as evidence that the dried-out plants had sprouted from their root crowns in response to rain [6].

Sheltered microsites appear to aid slenderhorn spineflower seedling establishment. In western Riverside and San Bernardino counties, crevices by rocks imbedded in the soil surface were favored establishment sites. At a former dumpsite, partially buried trash served the same function; in both cases, crevices likely trapped seeds and retained moisture [6]. Similarly, slenderhorn spineflower establishment might have been facilitated by the presence of woody plants after a fire on the Cleveland National Forest.

Because slenderhorn spineflower is an annual, population sizes fluctuate widely across and within years [6,19]. Over 3 years in western Riverside and San Bernardino countries, slenderhorn spineflower seedlings established throughout the growing season after intermittent rainstorms. Due to dry conditions between rains, many plants died before setting seed; plants establishing early in the growing season apparently had highest survival. Monthly population size was positively correlated with precipitation from the previous month (P=0.003) [6]. Establishment may be poor during drought years [19]. However, density of a population in Los Angeles County was not directly correlated with rainfall (Sapphos Environmental, Inc. 2008 cited in [19]).

Disturbance may promote establishment [19]; slenderhorn spineflower establishment was noted in tire tracks on a site near San Jacinto (Meyer personal communication cited in [1]). Near the Santa Ana River, slenderhorn spineflower establishment was noted in slight depressions that may have originated from rodent burrowing [23]. In western Riverside and San Bernardino counties, herbivory reduced slenderhorn spineflower growth and reproduction in some years. Floral stems were favored, while leaves were rarely consumed. The authors surmised that cyclically high numbers of grasshoppers were responsible for the herbivory [6].

Field studies in western Riverside and San Bernardino counties suggest that within a growing season, slenderhorn spineflower sprouts from the root crown after die-back from drought [6].

FIRE ECOLOGY:
Postfire regeneration strategy [15]:
Herbaceous root crown, growing points in soil
Ground residual colonizer (on site, initial community)
Crown residual colonizer (on site, initial community)
Initial off-site colonizer (off site, initial community)
Secondary colonizer (on- or off-site seed sources)

Fire adaptations and plant response to fire:
Fire adaptations: Slenderhorn spineflower establishes solely from soil-stored seed. Its seed bank is likely long-lived [5], so it may establish from seed after fire or other disturbances [19]. Animals and/or sheet erosion may aid in seed dispersal from off-site parent plants (see Establishment).

Postfire growth and seed production may depend partly on season of fire. Slenderhorn spineflower is unlikely to have time to reproduce after late-summer fire. In field studies, plants that died back completely in response to summer drought apparently sprouted from their root crowns after later summer rains, but they produced relatively few seeds [6]. This suggests that within a growing season, slenderhorn spineflower plants might resume growth after top-kill from fire, but seed production would be low. Next-year recruitment from the soil seed bank is probably more important for slenderhorn spineflower’s postfire regeneration than current-year sprouting and subsequent seed set.

Plant response to fire: Limited information suggests that fire may benefit slenderhorn spineflower populations. The US Fish and Wildlife Service [19] reports that wildfires in the Agua Tibia Wilderness-Vail Lake area of the Cleveland National Forest “have burned over occupied Dodecahema leptoceras habitat in the past with no apparent adverse effect; in fact, the observed number of plants increased dramatically after fire”. Postfire monitoring of slenderhorn spineflower was conducted following the August 1989 Vail Wildfire in the Aqua Tibia Wilderness Area. Plants established in burned areas during postfire year 1. Populations on both sides of a creek were expanding, and many large plants (10-12 inches (25-30 cm) diameter) were apparent. In September of 1994 (postfire year 5), both populations had >300 plants. The populations were concentrated near woody plants: a large oak tree on one bank and a clump on chamise on the other [22], suggesting possible facilitation by the woody plants. Most slenderhorn spineflowers were of “fairly good size”—about 2 to 3 inches (5-8 cm) in diameter—with around 20 achenes/plant [22].

The long-term fire response of slenderhorn spineflower was unknown as of 2013.

The Fire Regime Table summarizes characteristics of fire regimes for vegetation communities in which slenderhorn spineflower may occur. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".

LEGAL STATUS AND MANAGEMENT:
Federal legal status:
Endangered [20]

Other status:
State of California: Endangered (S1) [12]

Information on state-level protection status of plants in the United States and Canada is available at NatureServe.

Other management:
Loss of the old, stable alluvial scrub habitat where slenderhorn spineflower occurs is the primary threat to the species. Urban development and sand and gravel mining can directly degrade or eliminate habitat and encourage establishment of nonnative plants [19]. Slenderhorn spineflower is documented growing with nonnative grasses but at lower densities than on sites without nonnative grasses [1]. Urban flood control measures alter natural flood events necessary for maintaining suitable slenderhorn spineflower habitat. These measures may eliminate habitat and isolate slenderhorn spineflower populations [19].

Other threats to slenderhorn spineflower include soil disturbance from off-highway vehicle (OHV) usage, trash dumping, and trails created by unauthorized human activities near alluvial habitats [19].

Conservation efforts focusing on protecting existing slenderhorn spineflower populations and their habitats are recommended. Limited seed bank studies suggest artificial establishment of new populations may require a large investment of seeds over many generations before slenderhorn spineflower establishes naturally [5]. Slenderhorn spineflower plants have shown low seed production in the greenhouse [6,21]. Ferguson and others [6] were unable to raise slenderhorn spineflower plants to maturity despite easy germination.

For restoration purposes, soil and nonnative grass species in the proposed habitat should be considered before planting slenderhorn spineflower seed. Ideal sites would have silt (not loam) soil with pH around 6.4 and low electrical conductivity, with no annual grasses present [1]. In light of their difficulties in growing slenderhorn spineflower in the greenhouse, Ferguson and others [6] call for further studies on artificial regeneration of slenderhorn spineflower. They note that “natural recruitment from seed is no problem within populations, but the exact conditions for growing plants ex situ remain elusive” [6].

Further research is needed on all aspects of slenderhorn spineflower ecology.

APPENDIX: FIRE REGIME TABLE

SPECIES: Dodecahema leptoceras
The following table provides fire regime information that may be relevant to slenderhorn spineflower habitats. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".

Fire regime information on vegetation communities in which slenderhorn spineflower may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [11], which were developed by local experts using available literature and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)		 Minimum interval
(years)		 Maximum interval
(years)
California Shrubland
Chaparral Replacement 100% 50 30 125
Coastal sage scrub Replacement 100% 50 20 150
Coastal sage scrub-coastal prairie Replacement 8% 40 8 900
Mixed 31% 10 1 900
Surface or low 62% 5 1 6
California Woodland
California oak woodlands Replacement 8% 120    
Mixed 2% 500    
Surface or low 91% 10    
*Fire Severities—
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [3,10].

REFERENCES:

1. Allen, Edith B. 1996. Characterizing the habitat of slender-horned spineflower (Dodecahema leptoceras). Ecological analysis. Contract No. FG-4632-R5. Final report: April 1, 1995 to June 30, 1996. Long Beach, CA: California Department of Fish and Game, Region 5. 12 p. [+ appendices]. [86503]
2. Baldwin, Bruce G.; Goldman, Douglas H.; Keil, David J.; Patterson, Robert; Rosatti, Thomas J.; Wilken, Dieter H., eds. 2012. The Jepson manual. Vascular plants of California, second edition. Berkeley, CA: University of California Press. 1568 p. [86254]
3. Barrett, S.; Havlina, D.; Jones, J.; Hann, W.; Frame, C.; Hamilton, D.; Schon, K.; Demeo, T.; Hutter, L.; Menakis, J. 2010. Interagency Fire Regime Condition Class Guidebook. Version 3.0, [Online]. In: Interagency Fire Regime Condition Class (FRCC). U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy (Producers). Available: http://www.frcc.gov/. [85876]
4. California Native Plant Society. 2012. Inventory plant detail: Astragalus albens, [Online]. In: Inventory of rare and endangered plants. Version v8-01a. Sacramento, CA: California Native Plant Society (Producer). Available: http://www.rareplants.cnps.org/detail/292.html [2012, November 27]. [86302]
5. Ferguson, Nancy J.; Ellstrand, Norman C. 1999. Assessment of seed bank buffering of genetic change in Dodecahema leptoceras (slender-horned spineflower). Contract No. FG-7642R5. Long Beach, CA: California Department of Fish and Game, Region 5. 36 p. [86286]
6. Ferguson, Nancy.; Whitkus, Richard; Ellstrand, Norman C. 1996. Investigation into the population biology of Dodecahema leptoceras (slender-horned spineflower). Long Beach, CA: California Department of Fish and Game, Region 5. 25 p. [+figures]. [86525]
7. Gordon-Reedy, Patricia. 1997. Noteworthy collections, California. Madrono. 44(3): 305. [86510]
8. Hanes, Ted L.; Friesen, Richard D.; Keane, Kathy. 1989. Alluvial scrub vegetation in coastal southern California. In: Abell, Dana L., technical coordinator. Proceedings of the California riparian systems conference: Protection, management, and restoration for the 1990's; 1988 September 22-24; Davis, CA. Gen. Tech. Rep. PSW-110. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station: 187-193. [13882]
9. ITIS Database. 2013. Integrated taxonomic information system, [Online]. Available: http://www.itis.gov/index.html. [51763]
10. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: https://www.landfire.gov /downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. [66741]
11. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: https://www.landfire.gov /models_EW.php [2008, April 18] [66533]
12. NatureServe. 2013. NatureServe Explorer: An online encyclopedia of life, [Online]. Version 7.1. Arlington, VA: NatureServe (Producer). Available http://www.natureserve.org/explorer. [69873]
13. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]
14. Reveal, James L. 1989. Three new monospecific genera of Polygonaceae subfamily Eriogonoideae from California. Phytologia. 66(2): 83-88. [86504]
15. Stickney, Peter F. 1989. Seral origin of species comprising secondary plant succession in northern Rocky Mountain forests. FEIS workshop: Postfire regeneration. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. [20090]
16. The International Plant Names Index (IPNI). 2013. International Plant Names Index database, [Online]. The Royal Botanic Gardens, Kew; The Harvard University Herbaria; Australian National Herbarium (Producers). Available: http://www.ipni.org/index.html. [62970]
17. The Jepson Herbarium. 2013. Jepson online interchange for California floristics, [Online]. In: Jepson Flora Project. Berkeley, CA: University of California, The University and Jepson Herbaria (Producers). Available: http://ucjeps.berkeley.edu/interchange.html [70435]
18. U.S. Department of Agriculture, Natural Resources Conservation Service. 2013. PLANTS Database, [Online]. Available: https://plants.usda.gov /. [34262]
19. U.S. Department of Interior, Fish and Wildlife Service, Carlsbad Fish and Wildlife Office. 2010. Dodecahema leptoceras (slender-horned spineflower). 5-year review: summary and evaluation. Carlsbad, CA: U.S. Department of Interior, Fish and Wildlife Service, Carlsbad Fish and Wildlife Office. 37 p. [86505]
20. U.S. Department of the Interior, Fish and Wildlife Service. 2016. Endangered Species Program, [Online]. Available: http://www.fws.gov/endangered/. [86564]
21. Winter, Kirsten J. 1991. Slender-horned spineflower (Dodecahema leptoceras). Survey and monitoring, Cleveland National Forest. [San Diego], CA: U.S. Department of Agriculture, Cleveland National Forest. 12 p. [86508]
22. Winter, Kirsten. [1994]. Dodecahema leptoceras observation notes. Unpublished notes on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 1 p. [86507]
23. Wood, Yvonne; Wells, Stephen G. 1997. Characterizing the habitat of slender-horned spineflower (Dodecahema leptoceras): geomorphic analysis. Final Report. [Long Beach, CA]: [U.S. Department of Interior, Fish and Wildlife Service]. 57 p. [+ appendices]. [86502]
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