Overview
The Bartram’s stonecrop (Graptopetalum bartramii) was listed as threatened without designated critical habitat on August 31, 2021 under the Endangered Species Act of 1973, as amended. The taxon is known from Cochise, Pima, and Santa Cruz counties of southern Arizona, as well as Sonora and Chihuahua, Mexico. We are aware of 4,628 adult individuals across the entire range within the United States and Mexico, including an assumed 10 plants from two U.S. populations in Gardner Canyon East and Thomas Canyon, and one Mexico population, in Sierra La Estancia, that have had no population counts and have not been revisited since the initial survey took place. These are presumed to be extant, but small. There are no long-term monitoring plots with sufficient data to determine trends in the species, though we are aware that population numbers seem to fluctuate annually, especially within seedling and juvenile stages. We also are aware that many populations have been observed at the same locations over several decades and are persisting and self-sustaining. Other populations have been lost primarily due to flooding, loss of overstory trees or general drying of habitat. Threats from non-native plant invasion and alteration of fire regimes, drought and climate change climate change
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Scientific Name
Identification Numbers
Characteristics
Habitat
Bartram’s stonecrop is typically found in deep, narrow, heavily shaded canyons with erodible soils within Madrean woodlands at elevations ranging from 1,067 to 2,073 meters. Bartram’s stonecrop plants are almost always located near water sources like springs, seeps or intermittent streams, but above the floodline. This proximity to water, coupled with shade from trees and rock walls and a deep litter layer, collectively provide increased humidity and decreased temperature in the plant’s microclimate.
Land covered by evergreen trees in cool, northern latitudes. Also called taiga.
Physical Characteristics
The Bartram’s stonecrop is a small, perennial plant in the stonecrop family Crassulaceae. The species has a succulent basal rosette that is 7 to 16 centimeters wide and is comprised of 20 or more flat to concave, smooth, blue-green leaves with a waxy coating. During the fall, Bartram’s stonecrop produce one to seven showy flowering stalks that are up to 30.5 centimeters in height. The number of flowers per stalk and the number of stalks depends on the size and age of the plant with larger older plants having numerous stalks and up to 214 flowers. Flowers are yellow-petaled with brown-red dots that resemble writing, hence the scientific name Graptopetalum, meaning written on petals. The fruits are capsules that, in November and December, split along the side to release minute seeds that are less than 1 millimeter wide and resemble dust.
Life Cycle
Bartram’s stonecrop flowering is triggered by fall rains and does not occur during periods of water stress. Although Bartram’s stonecrop adult and immature plant numbers fluctuate annually pending drought and other threats, seedling numbers can fluctuate even further due to the vulnerability of this life stage to desiccation.
Bartram’s stonecrop flowering stalks grow in July and August with flowers produced in September to November. Individual Bartram’s stonecrop flowers open in succession, such that the length of time each flower remains open overlaps, allowing for various stages of flowering and fruiting to be simultaneous within an individual plant for a month or more. Bartram’s stonecrop seeds may be dispersed via water, gravity and wind. It is generally thought that the Bartram’s stonecrop soil seedbank may last one to two years under field conditions, with most germination occurring the year following seed production. Bartram’s stonecrop does not reproduce vegetatively and is dependent on pollinators and seed production for reproduction. Winter precipitation is needed for Bartram’s stonecrop germination, though some germination likely occurs following summer rains, and both summer and fall precipitation is needed for flower production.
The lifespan of Bartram’s stonecrop is thought to be approximately five years. This was determined from three individuals that were first measured in 2013, still being alive and mature in 2017. We are aware of several populations that have been observed at or near their originally observed location over time, which indicates that these populations are persisting and are self-sustaining over a period of several decades.
Geography
The current range of Bartram’s stonecrop includes nine mountain ranges with 47 populations in Cochise, Pima and Santa Cruz counties of southern Arizona, as well as three mountain ranges with one population each in Sonora and Chihuahua, Mexico.
Timeline
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