aka nodding beggarticks, sticktight; Bidens cernua; Asteraceae (aster family)
I found this annual plant along the sandy, exposed bed of the river when it was running very low, in mid-September. Although bur marigold likes really wet soils, it is not considered an emergent aquatic.
It can be found through most of the US and Canada, except for a few states in the south. Some authorities consider it weedy.
The more I see of composites, there more fascinated I am by them. Here’s a close up of the disk flowers.
By the way, it’s possible I’ve mis-identified this one. There’s another, almost identical species called smooth bur marigold (Bidens laevis); I spent a long time poring over details on the fantastic New England Wild Flower Society and John Hilty’s Illinois Wildflowers websites. These have become my go-tos whenever the books fail me.
aka devil’s beggar-ticks; Bidens frondosa; Asteraceae (aster family)
At this time of year the asters are just about the only things blooming in the Potomac gorge. This one is comprised entirely of disk flowers; the rays absent. The green parts surrounding the flower head are bracts.
According to the USDA, there are 26 species (one of them alien) of Bidens found in North America. Another one is Spanish needles, fotd 9/12. This one is probably the most widespread of them. It prefers moist soils and full sunlight but can tolerate some dry and shade; it’s prone to becoming a nuisance plant. While looking into the origin of the common name I tripped across a New Zealand website that featured it as Weed of the Month.
The common name comes from the fact that the seeds hitch a ride on the fur (or clothing) of passing animals.
Bidens bipinnata; Asteraceae (aster family)
[regular blog entries on hiatus until late September]