Mystery plant Devil’s beggar-ticks

(Question)

209gardenplants 001Hi, I’ve been unable to identify this plant that seems to pop up all over my garden. I let some go just to see what happened and I now have a plant that’s about 2 metres tall with tiny insignificant flowers now visible. The stem is about an inch in diameter, reddish with fine hairs. Branches come off every several inches in opposite pairs at right angles to the ones above and below. Seems to be ok with dry, crappy soil and tolerates shade, but doesn’t get as tall there. Any ideas would be helpful. Thanks, Heather

 

(Answer)

It looks very much like beggar’s ticks (Bidens frondosa).  If you can find the seeds (fruit) and they are the same as described below, then that is what you have.

Bidens frondosa is an annual herb that is usually about 20 to 60 (8-20 inches) centimeters tall, but it can reach 1.8 meters (72 inches or 6 feet) at times. The stems are square in cross-section and may branch near the top. The leaves are pinnate, divided into a few toothed triangular or lance-shaped leaflets usually up to 6 or 8 centimeters long, sometimes up to 12. The inflorescence is often a solitary flower head, but there may be pairs or arrays of several heads. The head contains many orange disc florets. It often lacks ray florets but some heads have a few small yellow rays. The fruit is a flat black or brown barbed cypsela up to a centimeter long which has two obvious hornlike pappi at one end which help them stick to animals.  This helps to dispurse the seeds.