Tickseed beggarticks at Sewickley Heights Park, 11 Sept 2026 (photo by Kate St. John)

20 September 2026

This flower is a closeup from the field of yellow flowers at Sewickley Heights Park. Tickseed beggarticks or bearded beggarticks (Bidens aristosa) are pretty flowers but they make annoying seeds.

The path of yellow flowers on the Pipeline Trail at Sewickley Heights Park during 3RBC outing, 11 Sept 2026 (photo by Kate St. John)

Fertilized flowers create “hitchhiker” seeds, each with two barbed prongs that grab whatever that brushes past the plant.

Beggarticks’ seeds, Bidens aristosa (photo from Wikimedia)

For instance, my sweater.

Beggarticks on my sleeve, September 2010 (photo by Kate St. John)

Beggarticks have a close relative that is also in bloom now. Spanish needles (Bidens bipinnata) have small yellow flowers and much longer seeds.

Spanish Needles (Bidens bipinnata) growing in the Beechview neighborhood of Pittsburgh (photo from Wikimedia)

Each seed is topped by a tiny pitchfork of two to four spikes with downward-facing barbs. They are too easy to pick up in passing.

Spanish Needles (Bidens bipinnata) growing in the Beechview neighborhood of Pittsburgh (photo from Wikimedia)

For instance, on another sweater.

Spanish needles on my sweater, Sept 2013 (photo by Kate St. John)

Late September is prime time for seedy hitchhikers.