A new population of the federally-endangered decurrent false aster

The target for today’s WGNSS Botany Group field trip was Boltonia decurrens (decurrent false aster), a federally endangered species known only from isolated stations along the Illinois River and near its confluence with the Mississippi River. The present population was discovered recently, although it was first collected from here almost 100 years ago, and it represents the northernmost known station of the species along the Mississippi River. We would find the plants flowering in abundance at the expected location, but before that we found an incredible stand of Helianthus grosseserratus (sawtooth sunflower) at the first meetup parking lot. This distinctive sunflower is recognized by its large, serrate, opposite leaves and glabrous or even glaucus purple stems. Some of the plants were enormous—one stood an estimated 14 feet tall.

Helianthus grosseserratus (sawtooth sunflower) inflorescence.
Helianthus grosseserratus (sawtooth sunflower) involucre.
Helianthus grosseserratus (sawtooth sunflower) stem/leaves.
The author stands next to a Helianthus grosseserratus (sawtooth sunflower) estimated at 14 feet tall.

Caravanning to the south end of the conservation area, it was a short hike to a thick stand of the decurrent false asters. Along the way, Cirsium discolor (field thistle) was blooming in abundance, it’s flowers a magnet for bumble bees and butterflies, especially Phoebis sennae (cloudless sulphurs or cloudless giant sulphurs).

Phoebis sennae (cloudless sulphur or cloudless giant sulphur) on inflorescence of Cirsium discolor (field thistle).

The stand of B. decurrens was visible from afar, forming a cloud of dense white flowers in the distance. The species is easy to distinguish from the only other species of the genus in Missouri by way of the flanges, or “wings,” that extend along the stem on each side below the leaf attachment. In some plants, the wings were poorly developed, leading to some speculation that they could represent hybrids with the much more common B. asteroides (white doll’s daisy), which occurs nearby and with which decurrent false aster is known to hybridize.

Boltonia decurrens (decurrent false aster).
Boltonia decurrens (decurrent false aster) inflorescences.
Boltonia decurrens (decurrent false aster) Inflorescence.
Boltonia decurrens (decurrent false aster) floret.
Boltonia decurrens (decurrent false aster) stem/leaves.

In the same general area, the asteracous hits kept on rolling with three species of Bidens (beggarticks/bur-marigolds). First was B. cernua (nodding bur-marigold), recognized by its large yellow ray florets and simple, opposite, clasping leaves.

Bidens cernua (nodding bur-marigold) inflorescence.
Bidens cernua (nodding bur-marigold) inflorescence.
Bidens cernua (nodding bur-marigold) involucre.
Bidens cernua (nodding bur-marigold) stem/leaves.
Bidens cernua (nodding bur-marigold) stem/leaves.

Next was what may have been B. aristosa (tickseed beggarticks) due to its small flowers with ray florets present and highly dissected, pinnately compound leaves, although it’s identity was never confirmed. Finally, along a nearby trail, we encountered B. vulgata (tall beggarticks), recognized by the small flowers with ray florets absent, numerous (>10) long phyllaries, and pinnately compound leaves.

Bidens aristosa (tickseed beggarticks) inflorescences.
Bidens aristosa (tickseed beggarticks) inflorescence.
Bidens aristosa (tickseed beggarticks) inflorescence.

I haven’t paid as much attention to aquatic plants as I should, but on this trip I benefitted from the willingness of a boot-clad Bruce to wade into a shallow pond and retrieve a Sagittaria calycina (Mississippi arrowhead, sometimes treated as a subspecies of S. montevidensis, or hooded arrowhead) for our examination. The species can be recognized by the pendent fruit clusters with persistent sepals strongly appressed to the clusters.

Sagittaria calycina (Mississippi arrowhead) inflorescence.
Sagittaria calycina (Mississippi arrowhead) flowers.
Sagittaria calycina (Mississippi arrowhead) leaf.
Sagittaria calycina (Mississippi arrowhead) fruits.

While we were looking at the Sagittaria, a Libytheana carinenta (American snout or common snout) butterfly posed cooperatively on Kathy’s thumb for photos.

Libytheana carinenta (American snout butterfly).

©️ Ted C. MacRae 2021