Common Names in English:
Dwarf Burr Ragweed, San Diego Ambrosia, San Diego Ragweed
The largest family of flowering plants , the Compositae (Asteraceae), comprising about 1,100 genera and more than 20,000 species and characterized by many small flowers arranged in a head looking like a single flower and subtended by an involucre of bracts. A head may consist of both ray flowers and disk flowers, as in the sunflower, of disk flowers only, as in the burdock, or of ray flowers only, as in the dandelion.
The Heliantheae are a tribe of closely related genera of the sunflower family that can be readily recognized due to the association of a receptacular bract or chaff scale with each disk floret in the head . The heads usually include bisexual , actinomorphic disk florets with tubular corollas that have 4 or 5 distal lobes and also peripheral zygomorphic female or sometimes sterile florets with strap-shaped corollas that have 3 or fewer distal teeth. However, the ray flowers are sometimes absent and the heads are then discoid , containing only bisexual florets with tubular corollas. The pappus is absent or more commonly ranges from scales to stiff bristles . -- Gerald Carr.
, or shrubs
, 10-400+ cm (usually rhizomatous
). Stems erect
, or prostrate
, branched. Leaves usually cauline; opposite ± throughout or opposite (proximal
) and alternate or mostly alternate; sessile or petiolate
) deltate, elliptic
, lanceolate, linear
, or rhombic
(and most intermediate shapes
), usually pinnately, sometimes palmately lobed
entire or toothed
, usually gland-dotted or stipitate-glandular
. Heads discoid
proximal to or intermixed with staminates
, staminates usually in racemiform
arrays; rarely, single plants
all or mostly staminate or pistillate). Pistillate heads: phyllaries 12-30(-80+) in 1-8+ series, outer (1-) 5-8 distinct
or ± connate
, herbaceous, the rest (sometimes interpreted as paleae) ± connate, usually with free
, spines, or wings
(the whole becoming a hard perigynium or "bur") ; florets
1(-5+), corollas 0. Staminate heads: involucres cup-shaped to saucer-shaped
, 1.5-6+ mm diam.; phyllaries 5-16+ in ± 1 series, ± connate; receptacles ± flat or convex
; paleae spatulate to linear, membranous, sometimes villous
, hirtellous, and/or gland-dotted or stipitate-glandular, sometimes none; florets 5-60+; corollas whitish or purplish, ± funnelform
, lobes 5, erect or incurved
distinct or weakly coherent. Cypselae (black) ± ovoid
, enclosed within globose
, obconic, or fusiform, hard, smooth
, or winged
"burs"; pappi 0. x = 18.
Species 40+: tropical to subtropical and temperate New World, mostly North America, some established in Old World.
Species Ambrosia pumila
Perennials , 10-20(-40+) cm. Stems erect . Leaves mostly alternate (sometimes crowded at bases of stems) ; petioles 5-35(-55) mm; blades deltate to elliptic , 15-35(-75) × 12-25(-45) mm overall, laciniately (1-) 2(-3) -pinnately lobed , bases cuneate to truncate , ultimate margins entire, abaxial and adaxial faces ± strigillose to sericeous (often grayish) and gland-dotted. Pistillate heads clustered, proximal to staminates ; florets 1. Staminate heads : peduncles 0.5-6 mm; involucres obliquely cup-shaped, 3-5 mm diam., ± strigillose; florets 8-25+. Burs: bodies ± fusiform , 2-2.5 mm, strigillose, spines or tubercles 0 or 1-5, mostly distal, stoutly conic, 0.1-0.5 mm, tips straight. 2n = 72. [source]
Flowers: Bloom Period: May, June, July, August, September, October.
Size: 18-24" tall.
sites, damp to wet, alkaline soils
; 100-200 m
San Diego ambrosia occurs in open habitats in coarse substrates near drainages , and in upland areas on clay slopes or on the dry margins of vernal pools . This species occurs in a variety of associations that are dominated by sparse grasslands or marginal wetland habitats such as river terraces , pools, and alkali playas (Munz 1974; Rieser 1996). In Riverside County, San Diego ambrosia is associated with open, gently-sloped grasslands and is generally associated with alkaline soils. Both extant Riverside County localities are found in close proximity to silty, alkaline soils of the Willows series (Knecht 1971). Preliminary testing of agricultural suitability of soils within a San Diego ambrosia population in San Diego County revealed mostly sandy loam textured soils, that were moderately acidic (pH ranging from 4.48 to 5.77) and low in salinity (DUDEK 1999). Control soil samples adjacent to this population where no San Diego ambrosia were present were more acidic ranging in pH from 3.97 to 4.63. Boling (1988) reported San Diego ambrosia from slopes from 0-9% slope on sandy or clay loams. At Mission Trails regional park in San Diego, Ambrosia pumila patches occurred upon slope angles ranging from 0 to 18% with the vast majority of plants occurring at slope angles of less than 5% (DUDEK 1999).
San Diego ambrosia generally occurs at low elevations generally less than 1600 feet in the Riverside populations and less than 600 feet in San Diego County (CNDDB; UCR database ; Munz 1974; Hickman 1993). Commonly associated species include Nasella spp. , Avena spp., Bromus spp., Centaurea melitensis, Ambrosia psilostachya , Hemizonia fascisulata, Holocarpha virgata, Distichlis spicata, Eremocarpus setigerus, and several vernal pool species (Burrascano 1997; DUDEK 1999).
Little published information is available concerning the reproductive
processes of San Diego Ambrosia. Ambrosia
pumila is a clonal, perennial
herb in the family
(Munz 1974; Payne 1993). Sexual reproduction and seed-set are not
considered to be common in this taxon
suggesting that propagation
by seed is limited. Propagation is primarily through
of rhizomes (underground stems) indicating that each population
could be a single plant and restricted
to the immediate appropriate
. Ambrosia pumila
to seasonal conditions and variation
causing the amount
of above ground
mass to fluctuate from year to year. Flowers are
generally present from June through September (Munz 1974). Ambrosia
species are probably primarily wind pollinated but other vectors
crawling insects) are a possibility (Payne, pers. comm.
Because pollen is contained in the downward facing male flower and
is positioned above female flowers Ambrosia
pumila is probably to a large extent self pollinating. Pollen
studies are needed to determine if out crossing is necessary for
viable seed production within Ambrosia
pumila (Burrascano 1997; Johnson, et al.
Ambrosia species generally produce
less seeds than annual species
in below ground root structures
(Payne 1962). Several biotechnical reports from transplantation efforts
for the lack of or low seed reproduction in the species
(Boling 1988; Marquez 1993; RECON 1993).
Preliminary analysis of seed viability have revealed little evidence of viable embryonic material (Ransom Seed Labs report in DUDEK1999). Although this study adds support to the low rate of sexual reproduction in San Diego ambrosia, a larger, multi-season sample needs to be collected to determine the viability of reproduction by seed.
Most technical studies and anecdotal accounts have reported preliminary success propagating San Diego Ambrosia from root material both in the nursery and in the field (Boling 1988; Marquez 1991-1993; RECON 1993; Bohn, pers. comm. 1998; Johnson, et al. 1999). Because San Diego ambrosia reproduces vegetatively and appears to be limited in its ability to sexually reproduce it probably is not a species capable of adapting to rapidly changing conditions. This may be a factor related to its limited distribution.
Low genetic diversity and low rates of sexual reproduction may be further diminished by propagation and transplantation. When small samples of root material are collected from insular populations and propagated and transplanted over larger areas, reproductive function problems may increase. Research concerning the genetic diversity and sexual reproduction of the plant is needed to answer basic questions about the biology and long term viability of this species.
Dispersal: Seed dispersal mechanisms for San Diego ambrosia are unknown. Because San Diego ambrosia is one of the few members of the Ambrosia genus that do not have armed involucral bracts it is less likely to disperse seeds by attaching to animals. Additionally, because the species has been reported to persist within horse corrals and is aromatic it may be unpalatable and unlikely dispersed by ungulate consumption . The species propensity to reproduce asexually suggests that the most common form of dispersal may be movement of rhizome-like structures either short distances by growth or longer distance by flood disturbance .
Culture: Space 15-18" apart.
Sunlight: Sun Exposure: Full Sun .
Temperature: Cold Hardiness: 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b. (map)
- Whittaker & Margulis,1978
- Haeckel, 1866
- Cavalier-Smith, 1981
- Sinnott, 1935 ex Cavalier-Smith, 1998
- Vascular Plants
- Brongniart, 1843
- Takhtajan, 1967
- Takhtajan Ex Reveal, 1992
- Lindley, 1833
- Family: Compositae () - Giseke, 1792, nom. cons., nom. alt.
- Order: Asterales () - Lindley, 1833
- Superorder: Campanulanae () - Takhtajan Ex Reveal, 1992
- Subclass: Asteridae () - Takhtajan, 1967
- Class: Spermatopsida () - Brongniart, 1843
- Subphylum: Euphyllophytina ()
- Phylum: Tracheophyta () - Sinnott, 1935 ex Cavalier-Smith, 1998 - Vascular Plants
- Subkingdom: Viridaeplantae () - Cavalier-Smith, 1981
- Kingdom: Plantae () - Haeckel, 1866 - Plants
Franseria pumila Nutt. • Franseria pumila Nuttall • N. s. 7: 344. 1840 • Trans. Amer. Philos. Soc.
Status: Accepted Name
Comment: Data Providers: CONABIO, Govaerts World Compositae Checklist A-G, IPNI, Tropicos. GCC LSID: urn :lsid:compositae.org:names:53C493D9-C004-4AFE-B4B1-ED0EEC159D26
Last scrutiny: 10-Aug-09
Genetics: Approximately forty-two species of the genus Ambrosia occur
in the western hemisphere primarily in arid regions of the southwest
United States and northern Mexico (Payne 1975). Twelve of these occur
in California and all but three are expected to occur in the Western
Riverside study area. San Diego ambrosia is closely related to A.
confertiflora, another herbaceous species with finely dissected
leaves and single-seeded fruit (Payne, et al. 1972). Species variability
is common within species of the Ambrosia in part because of the presence
of polyploid races and dysploidy (Payne 1976). Based on a sample
of San Diego ambrosia collected in San Diego County (Santee, CA)
the gametic (haploid) chromosome number is 72 (unpublished data from
Payne, et al. 1964). With the base 18, San Diego ambrosia in its
vegetative stage is an octoploid with 144 chromosomes. This may be
a mechanism for regularizing a hybrid background, which may serve
to reduce the plant’s adaptability by stabilization of the phenotype
( Payne, pers. comm. 1998).
Preliminary results from work by the Soil Ecology and Restoration Group (SERG) using electrophoretic gels suggests that two distant populations ( El Cajon, CA and the Sweetwater area in southern San Diego, CA) are genetically distinct and that genetic variation within each of these two populations is low (Johnson et al. 1999). Additional work concerning genetic variability of San Diego ambrosia is currently in progress from the SERG lab.
Members of the genus Ambrosia
ZipcodeZoo has pages for 36 species, subspecies, varieties, forms, and cultivars in this genus:
A. acanthicarpa (Annual Bursage) · A. ambrosioides (Ambrosia Bursage) · A. artemisifolia (Common Ragweed) · A. artemisiifolia (Annual Bur-Sage Ambrosia Artemisiifolia) · A. artemisiifolia L. var. artemisiifolia L. (Ragweed) · A. artemisiifolia L. var. paniculata (Michx.) Blank. (Annual Ragweed) · A. artemisiifolia var. artemisiifolia (Common Ragweed) · A. artemisiifolia var. elatior (Annual Ragweed) · A. artemisiifolia var. paniculata (Annual Ragweed) · A. bidentata (Lance-Leaf Ragweed) · A. canescens (Hairy Ragweed) · A. chamissonis (Beach-Bur) · A. cheiranthifolia (Rio Grande Ragweed) · A. chenopodiifolia (San Diego Ambrosia) · A. confertiflora (Ragweed) · A. cordifolia (Heartleaf Bursage) · A. deltoidea (Rabbit Bush) · A. dumosa (Burro Bush) · A. elatior var. elatior (Ragweed) · A. eriocentra (Hollyleaf Bursage) · A. grayi (Bur Ragweed) · A. helenae (Helen Ragweed) · A. hispida (Coastal Ragweed) · A. ilicifolia (Holly-Leaf Bursage) · A. intergradiens (Intergrading Ragweed) · A. linearis (Linear-Leaf Bursage) · A. peruviana (Peruvian Ragweed) · A. psilostachya (Cuman Ragweed) · A. pumila (Dwarf Burr Ragweed) · A. tenuifolia (Field Ragweed) · A. tomentosa (Bur Sage Ragweed) · A. trifida (Blood Ragweed) · A. trifida var. texana (Texan Great Ragweed) · A. trifida var. trifida (Great Ragweed) · A. × helenae (Helen Ragweed) · A. × intergradiens (Intergrading Ragweed)
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- 1997 IUCN red list of threatened plants Cambridge: IUCN, World Conservation Union, 1998 url p. 146.
- Britton, N. L. (ed.). North American flora. [New York]New York Botanical Garden. url p. 20.
- Compositae of southern California / by Harvey Monroe Hall. Berkeley, [Calif.]: The University Press, 1907. url p. 119.
- Flora of southern and Lower California: a check-list of the flowering plants and ferns / by Charles Russell Orcutt. San Diego, Calif.: [s.n.], 1885. url p. 6.
- Occasional papers - San Diego Society of Natural History. 1949 San Diego, The Society. url p. 145, p. 145.
- Proceedings of the Biological Society of Washington. Washington, Biological Society of Washington url p. 120, p. 120.
- Smithsonian miscellaneous collections. 31 1888 Washington: Smithsonian Institution, 1862-1968. url p. 250.
- Synoptical flora of North America. New York, American Book Company, 1878-1895/97 [v.2, pt. 1, 1878] url p. 250.
- Synoptical flora of North America: the Gamopetalæ, being a second edition of vol. I, part II, and vol. II, part I, collected. London, Iverson, Blakeman, Taylor, and Company;1886. url .
- Transactions of the San Diego Society of Natural History. 12 1959 [San Diego]: The Society, 1905-1989. url p. 382, p. 482.
- Ambrosia (Compositae). J. Arnold Arbor. 45: 401430.
- Payne, W. W. 1964. A re-evaluation of the genus
- Peterson, K. M. and W. W. Payne. 1973. The genus Hymenoclea (Compositae: Ambrosieae). Brittonia 25: 243256.
- Strother, J. L. and B. G. Baldwin. 2002. Hymenocleas are ambrosias (Compositae). Madroño 49: 143144.
- Brands, S.J. (comp.) 1989-present. The Taxonomicon. Universal Taxonomic Services, Zwaag, The Netherlands. Accessed January 10, 2012.
Accessed through GBIF Data Portal February 16, 2008:
- USDA PLANTS, USDA PLANTS Database
- Biodiversity Heritage Library NamebankID: 2657940
- Catalogue of Life Accepted Name Code: Ast-25404
- Global Biodiversity Information Facility Taxonkey: 13749025
- Globally Unique Identifier: urn:lsid:ipni.org:names:176124-1
- GRIN Nomen Number: 444529
- Integrated Taxonomic Information System (ITIS) Taxonomic Serial Number (TSN): 36517
- International Plant Names Index (IPNI) ID: 176124-1
- Natural Heritage Network Species Identifier: PDAST0C0M0
- U.S. Fish and Wildlife Service Species Identifier: Q01H
- U.S.D.A. Plant Symbol: AMPU4
- Zipcode Zoo Species Identifier: 20791