Asimina tetramera, commonly known as the four-petal pawpaw, is a rare species of small tree or perennial shrub endemic to Martin and Palm Beach Counties in the state of Florida. The species is currently listed as endangered under the Endangered Species Act and as endangered by the International Union for Conservation. The four-petal pawpaw is part of the Annonaceae family alongside other Asimina species.
A. tetramera grows to between 1 and 3 meters tall with one or more branches. Mature flowers are maroon with some pink streaks and the fruit is yellow-green. It usually has six petals and four sepals.
It lives exclusively in sand pine scrub habitat on the Atlantic Coast Ridge. A. tetramera is pollinated primarily by beetles which feed on tissue on the surface of its stamens and on the inner surface of its petals.
A. tetramera is a fire adapted species. The shrub grows best without the presence of a taller plant canopy shading it. A wildfire may remove these plant canopies to allow for the four-petal pawpaw to flourish. With the return of a shading canopy, the plant growth slows. The removal of the above-ground parts of the plant allows it to grow after a disturbance such as wildfire.
The small range of A. tetramera has been threatened by habitat loss and fire suppression for decades. Human development and disruptive activities has removed suitable land where the species can live. Also, the prevention of wildfires in Florida has limited its ability to grow and reproduce. Work is being done to protect and restore the four-petal pawpaw and its habitat. By protecting existing populations, performing controlled burns, and planting new A. tetramera within its native range, conservationists hope to prevent this rare shrub from going extinct.
Description
The four-petal pawpaw (Asimina tetramera) is a large shrub or small tree. Its fruit is aggregate and yellow-green in color. The fruit is banana-scented when ripe. The seeds of the plant are flat, shiny, and dark brown. The four-petal pawpaw is sensitive to transplantation due to its deep taproot.
Size and Coloration
It is classified as a large shrub or a small tree. Its growth habit ranges from a small tree or a larger perennial shrub. When sprouting, they are about 2 to 3 centimeters tall from the underground taproot. The plant height ranges from 1 to 3 meters tall. This makes it one of the tallest species of pawpaw.
A mature individual has one or more main stems in the plant. The colors of the branched or unbranched stems vary. This includes red, reddish-brown, brown, grayish-brown, and gray colored bark. The plant has pale lenticels.
The flowers of the four-pawpaw are maroon with occasional pink streaks. At the start of blooming, they can be seen with cream-colored flowers. The color of the flower changes as it ages. The fruit that the plant produces is yellow-green and aggregate.
Leaf Morphology
The leaves of A. tetramera have an oblong shape and alternate in a spiral pattern on the stem. They measure about 5–10 cm in length. The tips of the leaves are usually blunt. The leaf margins of A. tetramera roll under. This means the leaves of the plant have rolled edges. Young leaves are spotted with small reddish hairs. As they age, the leaves turn to a dark green with a smooth surface. The undersides of the leaves are gray-green in color. The undersides are also reticulated as opposed to the smooth top side of the leaf.
Flower Structure
A. tetramera has 6 petals split into two sets of three. Usually the petals are three-merous, as said before; however, there is evidence of some four-merous flowers in this species. It has four sepals. A. tetramera has a unique number of sepals since other Asimina species only have three. The stamens are arranged in a spiral pattern on the receptacles. The receptacles of the flower have separate carpels. The outer petals of the flower are about 1.5 to 3 centimeters long. They are oblong oval shaped.
Life History
Development
A. tetramera grows a deep taproot. The root crown permits the survival of the plant through droughts, wildfires, and other disturbances. If the aboveground parts of the plant are removed, the plant can resprout from the intact roots.