Ambrosia pumila
Encyclopedia
Ambrosia pumila is a rare species of ragweed
known by the common names dwarf burr ragweed and San Diego ambrosia. It is native to far southern California
and Baja California
where it grows in floodplain
s and scrub. Today it is known from 19 populations. Fourteen of them are in San Diego County
, two exist in Riverside County
, and there are three south of the border in Mexico. Most of its native habitat has been consumed by urbanization and development. It is also threatened by agriculture
. This is a federally listed endangered species
of the United States.
This is a hairy perennial herb not exceeding half a meter in height. The leaves are gray-green and fuzzy and divided into several subdivided segments. They are up to 13 centimeters long, not counting the winged petioles
. The inflorescence
is tipped with staminate
(male) flower heads
above several larger pistillate
(female) heads. The pistillate heads each yield usually one fruit, which is a fuzzy burr
only a few millimeters wide with short, soft spines. The plant rarely produces seeds. The plant reproduces vegetatively
, sending up new sprouts from an elongated rhizome
system.
Critical habitat was declared for the species in 2010, listing areas that should be protected for the survival of the plant. It is adapted to dry habitat, but only on floodplains that are periodically submerged, or in depressions containing vernal pool
s or similar structures. It is a plant of open habitat and is probably not tolerant of shade. Protected areas containing this plant include sections of land in the cities of Temecula
and Oceanside
, near Fallbrook
and Lake Hodges
, and within the bounds of Mission Trails Regional Park
and the San Diego National Wildlife Refuge
.
One threat to the species is the invasion of non-native weeds
, which tower over the plant and shade it out. It is challenging to remove the dense stands of weeds without injuring the rare plant.
Ragweed
Ragweeds are flowering plants in the genus Ambrosia in the sunflower family Asteraceae. Common names include bitterweeds and bloodweeds....
known by the common names dwarf burr ragweed and San Diego ambrosia. It is native to far southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
where it grows in floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
s and scrub. Today it is known from 19 populations. Fourteen of them are in San Diego County
San Diego County, California
San Diego County is a large county located in the southwestern corner of the US state of California. Hence, San Diego County is also located in the southwestern corner of the 48 contiguous United States. Its county seat and largest city is San Diego. Its population was about 2,813,835 in the 2000...
, two exist in Riverside County
Riverside County, California
Riverside County is a county in the U.S. state of California. One of 58 California counties, it covers in the southern part of the state, and stretches from Orange County to the Colorado River, which forms the state border with Arizona. The county derives its name from the city of Riverside,...
, and there are three south of the border in Mexico. Most of its native habitat has been consumed by urbanization and development. It is also threatened by agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
. This is a federally listed endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of the United States.
This is a hairy perennial herb not exceeding half a meter in height. The leaves are gray-green and fuzzy and divided into several subdivided segments. They are up to 13 centimeters long, not counting the winged petioles
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...
. The inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
is tipped with staminate
Stamen
The stamen is the pollen producing reproductive organ of a flower...
(male) flower heads
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
above several larger pistillate
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
(female) heads. The pistillate heads each yield usually one fruit, which is a fuzzy burr
Burr (fruit)
A bur is a seed or dry fruit in which the seeds bear hooks or teeth which attach themselves to fur or clothing of passing animals or people. The hooks or teeth can be irritants and very hard to get off of clothing, such as wool or cotton...
only a few millimeters wide with short, soft spines. The plant rarely produces seeds. The plant reproduces vegetatively
Vegetative reproduction
Vegetative reproduction is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores...
, sending up new sprouts from an elongated rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
system.
Critical habitat was declared for the species in 2010, listing areas that should be protected for the survival of the plant. It is adapted to dry habitat, but only on floodplains that are periodically submerged, or in depressions containing vernal pool
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
s or similar structures. It is a plant of open habitat and is probably not tolerant of shade. Protected areas containing this plant include sections of land in the cities of Temecula
Temecula, California
Temecula is a city in southwestern Riverside County, California, United States with a population of 100,097 according to the 2010 United States Census, making it the lowest populated American city over 100,000 population. It was incorporated on December 1, 1989...
and Oceanside
Oceanside, California
-2010:The 2010 United States Census reported that Oceanside had a population of 167,086. The population density was 3,961.8 people per square mile...
, near Fallbrook
Fallbrook, California
Fallbrook is an unincorporated community in northern San Diego County, California. The Fallbrook census-designated place population was 30,534 at the 2010 census, up from 29,100 at the 2000 census....
and Lake Hodges
Lake Hodges
Lake Hodges is a lake and reservoir located in Southern California, about north of San Diego and just south of Escondido, California. When full, the reservoir has , a maximum water depth of , and of shoreline. Interstate 15 crosses Lake Hodges via the Lake Hodges Bridge...
, and within the bounds of Mission Trails Regional Park
Mission Trails Regional Park
Mission Trails Regional Park is a 5,800 acre open space preserve within the city of San Diego, California, established in 1974. It is the sixth largest municipally-owned park in the United States, and the largest in California.-Description:...
and the San Diego National Wildlife Refuge
San Diego National Wildlife Refuge
San Diego National Wildlife Refuge is a National Wildlife Refuge in California. It is part of the San Diego National Wildlife Refuge Complex.A variety of habitats from coastal sage scrub and chaparral to oak woodland and freshwater marsh describe this inland refuge in San Diego's backcountry.The...
.
One threat to the species is the invasion of non-native weeds
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
, which tower over the plant and shade it out. It is challenging to remove the dense stands of weeds without injuring the rare plant.
External links
Further reading
- McGlaughlin, M. E. and E. A. Friar. (2007). Clonality in the endangered Ambrosia pumila (Asteraceae) inferred from RAPD markers; Implications for conservation and management. Conservation Genetics 8:2 319.