Symphyotrichum depauperatum, the Serpentine Aster, may be the most unusual native aster in North Carolina. It is extremely rare, with a state ranking of Critically Imperiled, and a status of Endangered . In addition, it is found at only a single site (Granville County) in North Carolina. Also remarkable and unique is its occurrence on a diabase glade in North Carolina. All other populations in North America are found on serpentine barrens, primarily in Maryland and Pennsylvania. Its occurrence on serpentine soils (more about this later) gave rise to the common name of Serpentine Aster.
Symphyotrichum depauperatum is a diminutive, fragile aster with thin stems, and small flowers. The flowers have 7 to 14 white rays and yellow discs. The leaves on the flowering stems are tiny, narrow and sharply pointed. See below.
The plant above is shown below with a hand in the photo to demonstrate its small size.
Below is another fully developed aster against the backdrop of a camera case. The photo shows a typical blooming form of the Serpentine Aster. The camera case is 8 inches tall.
The basal leaves in this group of asters were quite variable, but tended to be rounded in the newer leaves, and lanceolate to spatulate in the more developed leaves. The first photo below shows the basal leaves just emerging and the second photo shows an older aster whose basal leaves are mature. Also note the ciliate (fine hair) leaf margins in the two photos below.
As with many perennial asters, the basal leaves wither when the aster begins to bloom, but new basal leaves develop to take their place. Red arrows in the photo below show the basal leaves that have just withered, underneath the newly arrived leaves. The ciliate leaf margins are still visible on some.
As mentioned above, the occurrence of the Serpentine Aster in a diabase glade is very unusual. Serpentine barrens are harsh and demanding ecosystems that arise on serpentine soils derived from underlying serpentonite rock. In the U.S., most occur in Maryland, Pennsylvania, and California. They are characterized by shallow soils with a low nutrient content, low water holding capacity, high magnesium and low calcium (an unfavorable ratio for plants), and high levels of metals like chromium and nickel. Thus it is no surprise that the species name for the Serpentine Aster, depauperatum, is derived from the Latin for impoverished or starved.
While diabase soils can also be shallow and have a high Magnesium content, they generally have an adequate nutrient content and sufficient calcium for a favorable magnesium/calcium ratio. The Serpentine Aster’s presence at this site in North Carolina remains somewhat of a mystery.
For more on serpentine habitats see:
Intraspecific Variability in the Response of Certain Native Plant Species to Serpentine Soil. Arthur R. Kruckeberg, American Journal of Botany, Vol 38, No 6 (June, 1951) pp 408-419
Brian Anacker. 2014. The nature of serpentine endemism. American Journal of Botany. 101: 219-224.