Turkey oak, acorn on the tree, Schenley Park, 29 July 2026 (photo by Kate St. John)

2 August 2026

How many seed capsules can you think of that have “hitchhiker” hooks?

#1. I was puzzled by the acorn cup, pictured above, because I don’t know of any native northeastern oaks that have these hooks. The acorn is from a non-native Turkey oak (Quercus cerris) from southeastern Europe including Turkey. It was planted in Schenley Park at the top of the Serpentine Road more than 100 years ago.

#2. Those hooks reminded me of common burdock (Arctium minus), another non-native plant from Europe. The oak is not invasive but common burdock is.

Common burdock, 26 July 2026 (photo by Kate St. John)

#3. For native plants with hooks I thought of the sweetgum (Liquidambar styraciflua) seed ball even though its spikes are not very hooked at the tips.

Sweetgum seed ball, 18 November 2020 (photo by Kate St. John)

When the sweetgum ball dries out it is woody and spiky and very bad to step on with bare feet. Each sweetgum spike contains 1 or 2 seeds.

Sweetgum seed ball, 21 January 2022 (photo by Kate St. John)

#4. The other examples were large. These are small, the tiny hooked seed capsules of small flowered agrimony (Agrimonia parviflora). Agrimony branches dangle across the trail around knee height and readily grab onto your pant legs. They are at least slightly aggravating.

Agrimony seeds still on the stem, 23 July 2021 (photo by Kate St. John)

Can you think of other examples? If so leave a comment.