Shale-barren Aster (Symphyotrichum oblongifolium), white-flowered form

 

As always, click the photo to enlarge

Last Saturday, Shauna had to give a program on Bobcats to a group at the Arc of Appalachia's Highland Nature Sanctuary and following that we headed down to Lynx Prairie in Adams County to drum up some late-season flora. One species that was high on my list to photograph was Shale-barren Aster (Symphyotrichum oblongifolium). It is in peak bloom in early to mid-October, and we soon found ourselves admiring this large colony.

Shale-barren Aster is well-named, as can be seen from this image. It favors dry, rocky ground, and in Ohio often occurs on slopes like this. The plant is rhizomatous and can form sizable colonies. But in our state, it's a rarity and is listed as threatened by ODNR. Shale-barren Aster barely gets into southern Ohio and is known from only three-four counties and Adams County hosts most of the populations.

Here's the typical flowers of Shale-barren Aster. The rays are a showy pale purplish color, offset by bright yellow disk flowers.

PHOTO NOTE: Sometimes, to better isolate plants in crowded environments, I place a piece of black velvet behind the subject. That's what was done here. It also allows me to use a smaller aperture without penalty of creating a distracting image with lots of background clutter confusing the issue. This image was made at f/16, 1/125 second, and ISO 800. The only reason that the ISO was so high was due to breezy conditions and possible subject movement, but since very little cropping was required and the Canon R5 handles higher ISO settings well, it's not a problem. The lens was the stellar Canon 100mm f/2.8L macro.

As we walked towards the main colony, Shauna drew my attention to a white-flowered aster. Wow! It was an odd plant of Shale-barren Aster with snowy-white flowers! I had never seen, nor heard of such a thing. There were only three specimens, fairly close together and I suppose they could have essentially been the same plant, interconnected by rhizomes. This image shows the distinctive herbage, with alternate slightly clasping oblong leaves.

Here's a closeup of a flowering head. Not even a tinge of pink, purple or rose in those rays.

I've scouted about a bit and cannot find any references to white-flowered forms of Symphyotrichum oblongifolium. That's not to say it doesn't occur elsewhere, because anomalous white flowers regularly turn up in flowers that are ordinarily other colors. But it must not be common, or botanical manuals would mention it, and someone probably would have described it as a named form. The great botanist Merrit Fernald was big on noting variations such as this, yet his 1950 Gray's Manual of Botany makes no mention of white-flowered variants of Shale-barren Aster. He does note a forma roseoligulatus, which has rosy-colored rays. That, however, would be far more subtle and probably often insensibly grading into typical flower colors.

It will be interesting to see if these plants persist and expand, or eventually vanish.

NOTE: In botany, the equivalent of a subspecies in animals is termed a variety. Varieties are typically stable and distinctive variants but do not rise to the level of a species and are clearly closely related to the nominate, or typical variety. An example involving another aster would be Purple Swamp Aster (Symphyotrichum puniceum). It was long split into "subspecies": Symphyotrichum puniceum variety puniceum (the nominate, or typical, subspecies) and S. puniceum var. firmus. As sometimes happens, these two varieties were later shown to be distinct, and both are considered separate species now. Forms do not rise to that level and are minor variants. In the case of Purple Swamp Aster, two forms have been described, Symphyotrichum puniceum forma etiamalbus with white flowers, and forma rufescens with reddish flowers. These forms only different in flower color, thus are minor variations, and possibly best treated as occasional anomalies, not stable characters of the species, hence the forma designation. That's undoubtedly the case with the white-flowered Shale-barren Aster that we found.