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Plant Profile

San Diego Ragweed (Ambrosia pumila)

San Diego ambrosia (Ambrosia pumila) is a perennial herb that primarily inhabits grasslands and drainages in a small segment of San Diego County. It is listed as endangered under the Endangered Species Act. Photo Credit: Joanna Gilkeson/USFWS © 2017

Global Rank: G1 - Critically Imperiled
Legal Status: Federally Endangered
Family: Asteraceae
State: CA
Nature Serve ID: 154697
Lifeform: Forb/herb
Date Inducted in National Collection: 06/13/2017

Description:

Ambrosia pumilla is a species of ambrosia native to San Diego and Riverside counties. It is a low growing (2-12\") herbaceous perennial with fuzzy, feathery white-gray leaves that spreads through rhizomes. It forms clusters of genetically identical individuals and has a low level of viable seed set. It bears separate male and female flowers on a single plant and its fruit is a small single seeded achene. The aerial stems of Ambrosia pumilla sprout from the rhizomes following winter rains and they flower between May and October.The aerial stems senesce after flowering, with the rhizome remaining to sprout again when conditions are favorable.

Where is San Diego Ragweed (Ambrosia pumila) located in the wild?

Habitat:

Ambrosia pumilla grows primarily in the upper terraces of rivers and drainages. It also grow on the outer edges and near vernal pools. It is believed that flood waters may play a role in dispersing Ambrosia pumilla seeds and rhizomes. It grows in grassland and openings in coastal stage scrub within these habitats. It is typically found in clay or sandy loam soils.

Distribution:

There are currently 16 native occurences of Ambrosia pumilla in the United States, with 12 populations in San Diego County and 4 in Riverside County. This species is found in northwestern Baja California, Mexico as well. The populations occur at less than 1600' in Riverside County and less than 600' in San Diego County

States & Provinces:

San Diego Ragweed can be found in California

Which CPC Partners conserve San Diego Ragweed (Ambrosia pumila)?

San Diego Zoo Wildlife Alliance

Not Sponsored

Conservation Actions

Assigned 06/13/17

CPC's Plant Sponsorship Program provides long term stewardship of rare plants in our National Collection. We are so grateful for all our donors who have made the Plant Sponsorship Program so successful. We are in the process of acknowledging all our wonderful plant sponsorship donors on our website. This is a work in progress and will be updated regularly.

Conservation Actions

Katie Heineman

06/30/2021

In 1999, researchers at San Diego State University Soil Ecology Restoration Group translocated 1006 Ambrosia pumila individuals salvaged from the Sweetwater area of San Diego County to six planting sites in Los Penasquitos Canyon Preserve. http://www.sci.sdsu.edu/serg/restorationproj/chaparraland/ambrosia.html

A report published in Native Plants (Bainbridge 2007) indicates that nearly 10 years after salvage - genets were still alive at many translocation sites. Translocation success was linked to management of invasive plants and the extent of gopher herbivory.

https://ssl.rngr.net/publications/fnn/2007-summer/new-nursery-literature/salvaging-and-relocating-ambrosia-pumila

Katie Heineman

06/30/2021

Non-native plant species are considered a threat to most extant populations of Ambrosia pumila. In 2009, the Center for Natural Lands Management conducted an experiment testing how invasive species treatments (control, mowing, hand pulling, and Fusilade herbicide treatment) affect the number of A. pumila stems in treatment plots. The effectiveness of herbicide treatments depended on the identity of the invasive species at the plot - but maybe effective management practice are larger sites in conjunction with mowing. The results are summarized in detail in Hasselquist et al. 2013: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1526-100X.2012.00883.x

Katie Heineman

06/30/2021

Ambrosia pumila is a clonally reproducing species. McGlaughlin & Friar (2007) sampled Random Amplified Polymorphic DNA (RAPD) genetic markers from 201 stems in three Ambrosia populations. From these individuals, they found 31 unique genotypes, none of which were shared across multiple populations. Each population did contain multiple genotypes. Consequently, A. pumila’s clonal reproduction limits genetic diversity within populations and maintains strong variation in genetic structure between populations

09/01/2020

Based on an September 2020 extract of the California Plant Rescue Database, San Diego Zoo Global holds 1 accessions of Ambrosia pumila in orthodox seed collection. There are as many as 135 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

08/05/2020

Based on an August 2020 extract of the California Plant Rescue Database, San Diego Zoo Global has collected 1 seed accessions of Ambrosia pumila from 1 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 8 maternal plants