CPC Plant Profile: Mexican Flannelbush
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Plant Profile

Mexican Flannelbush (Fremontodendron mexicanum)

This shot shows the Mexican flannelbush leaves and flowers against the sky. Photo Credit: Dylan Hannon
Description
  • Global Rank: G1 - Critically Imperiled
  • Legal Status: Federally Endangered
  • Family: Malvaceae
  • State: CA
  • Nature Serve ID: 148726
  • Date Inducted in National Collection: 03/14/1986

Fremontodendron mexicanum is a tree-like shrub with bright yellow to orange flowers that bloom between March and August (USFWS 2009). The showy plant is often used as an ornamental shrub in gardens.

Participating Institutions
Updates
  • 10/16/2020
  • Reintroduction

Some introductions have taken place on the San Diego Natural Wildlife Refuge. Multiple individuals were planted in two separate locations. Neither introduction was very successful, though it is thought that they were unsuccessful as a result of the extreme prolonged drought that occurred in Southern California from 2011-2016. I believe that there are still several living individuals in the introductions. John Martin with the SDNWR has more information.

  • 10/16/2020
  • Propagation Research

Heat treatment the most successful pre-treatment in germination. See References below for citation, PDF available online.

  • 10/16/2020
  • Reproductive Research

Study published in 2014 by BC Austin with SDSU discussed the reproductive biology of the species, including pollinators, pollination success, seed dispersal, and germination success.

  • 10/16/2020
  • Living Collection

RSABG currently has five living plants from two accessions growing in the garden: Acc. 14425; cuttings collected in wild 1980; San Diego County: San Ysidro Mountains; 1 plant Acc. 15463; cuttings collected in wild 1986; San Diego County: San Ysidro Mountains; 4 plants

  • 10/16/2020
  • Propagation Research

Active propagation continues in the nursery at RSABG. In 2016, both softwood and semi-hardwood cuttings of Acc. 15463 were propagated by stripping off trichomes by hand and dipping in a 10% dilution of Wood's Rooting Hormone. In 2016, 20 plants were propagated from seed of Acc. 23212 using a hot water treatment and a cold-moist stratification.

  • 10/16/2020
  • Orthodox Seed Banking

he Seed Conservation Program at RSABG currently houses four seed collections of Fremontodendron mexicanum: Acc. 16824; 1985; Baja California: Maneadero; 21 seeds Acc. 15783; 1988; San Diego County: San Ysidro Mountains; 543 seeds Acc. 19682; 1997; San Diego County: San Ysidro Mountains; 67 seeds Acc. 23212; 2010; San Diego County: San Ysidro Mountains; 2276 seeds

  • 10/16/2020
  • Orthodox Seed Banking

San Diego Zoo Global has two maternal line seed collections. One collection was made from the smallest population in Little Cedar Canyon in 2016. The other was made from the largest population in Woodwardia Canyon in 2017. We plan on collecting from the third and final population in Cedar Canyon in 2018.

  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, San Diego Zoo Global holds 4 accessions of Fremontodendron mexicanum in orthodox seed collection. There are as many as 19464 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, California Botanic Garden holds 4 accessions of Fremontodendron mexicanum in orthodox seed collection. There are as many as 2907 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, San Diego Zoo Global has collected 4 seed accessions of Fremontodendron mexicanum from 3 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 243 maternal plants

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, California Botanic Garden has collected 4 seed accessions of Fremontodendron mexicanum from 2 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 50 maternal plants

Joe Davitt
  • 12/22/2017

San Diego Zoo Global has two maternal line seed collections. One collection was made from the smallest population in Little Cedar Canyon in 2016. The other was made from the largest population in Woodwardia Canyon in 2017. We plan on collecting from the third and final population in Cedar Canyon in 2018.

Joe Davitt
  • 12/22/2017

The US Fish and Wildlife 5-year review (USFW 2009) indicates that there are 3 populations in the US, occurring in 3 separate canyons, all on the north slope of Otay Mountain. The total number of individuals is roughly 6,000 individuals. The numbers appear stable, and in my opinion appear to be growing. In surveying I have seen many young trees and the populations seem to be doing well. That being said, they are all very localized, with all individuals occurring in roughly 11 square miles, and the threat of a single fire damaging all populations is great.

Joe Davitt
  • 12/22/2017

Study published in 2014 by BC Austin with SDSU discussed the reproductive biology of the species, including pollinators, pollination success, seed dispersal, and germination success. European honey bees were the predominate floral visitors, though native bees were present. The seeds are dispersed by seed harvesting ants, and potentially by flowing water. Heat treatment the most successful pre-treatment in germination. See References below for citation, PDF available online.

Joe Davitt
  • 12/22/2017

Some introductions have taken place on the San Diego Natural Wildlife Refuge. Multiple individuals were planted in two separate locations. Neither introduction was very successful, though it is thought that they were unsuccessful as a result of the extreme prolonged drought that occurred in Southern California from 2011-2016. I believe that there are still several living individuals in the introductions. John Martin with the SDNWR has more information.

Joe Davitt
  • 12/22/2017

The other major threat is the spread of invasive species that specialize in the rocky washes where Fremontodendron thrives. I have concern with the spread of Tamarix spp. which are prevalent in the washes, as well as Foeniculum (fennel) and many different grasses. 

Joe Davitt
  • 12/22/2017

Invasive weed removal in the canyon washes is also needed. Though difficult to access, the removal of Tamarix spp. and other invasives, will ensure the species is able to spread and potentially minimize the bio-load and fire risk.

Joe Davitt
  • 12/22/2017

We must first ensure that the breadth of the species genetic information is stored ex-situ. Research should then look at reintroduction methods.

  • 12/22/2017

All 3 populations occur on protected lands. Populations are monitored periodically, but are difficult to access. Some weed removal is done in some areas, but as they are so hard to access, it is minimal.

Joe Davitt
  • 12/22/2017

There are also two historic occurrences of the species in Mexico. The populations are believed small, and one may be extirpated.  Very little information is available.

Joe Davitt
  • 12/22/2017

The greatest threat to the species, in my opinion, is an increased fire frequency, as a result of invasive species. The 3 populations are in close proximity to one another and are very remote. A single large fire around Otay Mountain could threaten all known wild individuals. The species is adapted to fire, and is able to re-sprout after most fires. Invasive grasses have led to a greater intensity of fires, potentially resulting in fires that are so hot that the roots are destroyed and can no longer re-sprout. More problematic is the increase in fire frequency as a result of invasive grasses. Repeated burns in short succession can potentially decimate the populations in a very short amount of time.

Cheryl Birker
  • 12/18/2017

The Seed Conservation Program at RSABG currently houses four seed collections of Fremontodendron mexicanum:

  • Acc. 16824; 1985; Baja California: Maneadero; 21 seeds
  • Acc. 15783; 1988; San Diego County: San Ysidro Mountains; 543 seeds
  • Acc. 19682; 1997; San Diego County: San Ysidro Mountains; 67 seeds
  • Acc. 23212; 2010; San Diego County: San Ysidro Mountains; 2276 seeds

Cheryl Birker
  • 12/18/2017

Active propagation continues in the nursery at RSABG.
In 2016, both softwood and semi-hardwood cuttings of Acc. 15463 were propagated by stripping off trichomes by hand and dipping in a 10% dilution of Wood's Rooting Hormone. 
In 2016, 20 plants were propagated from seed of Acc. 23212 using a hot water treatment and a cold-moist stratification. 

Cheryl Birker
  • 12/18/2017

RSABG currently has five living plants from two accessions growing in the garden:

  • Acc. 14425; cuttings collected in wild 1980; San Diego County: San Ysidro Mountains; 1 plant
  • Acc. 15463; cuttings collected in wild 1986; San Diego County: San Ysidro Mountains; 4 plants

Nature Serve Biotics
  • 05/02/2017

Fremontodendron mexicanum is known with certainty only from southern San Diego County, California and south into Arroyo Seco (North of San Quintin) Baja California, Mexico. The plants have been relocated recently at only one of the twelve known sites despite searches of at least some of the historic locales. The California population is thought to contain fewer than one hundred individuals. The Bureau of Land Management specifically manages its land for this population; the Area of Critical Environmental Concern and the Research Natural Area, on which about 50% of the plant's habitat lies, were designated for the preservation of F. mexicanum. The species is likely susceptible to adverse genetic effects due to the low number of remaining individuals. Another primary threat is from altered fire regimes.

  • 01/01/2010

Competition for water with an annual ryegrass that was introduced by the Department of Forestry after a fire. Alteration of fire natural fire patterns is a threat to seedlings, seed banks and regrowth (USFWS 1998).

  • 01/01/2010

Less than 100 individuals are known from sites in San Diego County and Mexico. Reports of individuals growing in Los Angeles County are believed to be garden escapees (USFWS 1998).

  • 01/01/2010

The remaining population in San Diego County is under the protection of the Bureau of Land Management (BLM), however, BLM does not have control over the entire habitat. Efforts to control human foot traffic (a potential source of accidental fires) have not been successful (USFWS 1998).

  • 01/01/2010

Remaining populations are on privately owned land that need protection. In addition to better understanding the fire effects, research needs include reproductive biology and ecology.

MORE
Katie Heineman 04/19/2019

Our seedbank made a mini breakthrough this week with a new pretreatment for our germination trials of Fremontodendron mexicanum. After an initial trial that consisted of only imbibing yielded only a few germinants, we tried two treatments to weaken the seed coat: hot water and scratching the coat with sand paper. Both treatments dramatically increased germination. 

Photos
Nomenclature
Taxon Fremontodendron mexicanum
Authority A. Davids.
Family Malvaceae
CPC Number 1953
ITIS 21581
USDA FRME2
Common Names Mexican Flannelbush | Mexican Fremontia
Associated Scientific Names Fremontia mexicana | Fremontodendron mexicanum | Fremontia californica var. mexicana | Fremontodendron californicum subsp. mexicanum
Distribution This species is restricted to one site in San Diego County, its native range  (USFWS 1995, 1998). All individuals found outside of its native range in the U.S. are cultivated plants. One population in Arroyo Seco, Mexico was known at the time of this species' listing, but has been thought to be extirpated. More recently, a population in Arroyo Hediondo, Baja California, Mexico was found in 2000 with less than 20 individuals (USFWS 2009).
State Rank
State State Rank
California S1
Habitat

Fremontodendron mexicanum occurs in closed-cone coniferous forests dominated by Cupressus forbesii and with mixed chaparral in southern California (USFWS 1995). It is able to grow at elevations ranging from sea level to 1000 meters (USFWS 2009).

Ecological Relationships

Ecological relationships are widely unknown. There is circumstantial evidence for competition with an annual ryegrass and the possibility of negative effects incurred by frequent human caused fires (USFWS 1998).

Pollinators
Common Name Name in Text Association Type Source InteractionID
Bees
Honey bees Apis mellifera Confirmed Pollinator Link
Beetles
Flower beetles Melyridae Floral Visitor Link
Birds
Hummingbirds Hummingbirds Floral Visitor Link
Other
Hymenoptera Floral Visitor Link

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