Zizia and Thaspium

I have been on field trips with the Georgia Botanical Society where we encountered a yellow-flowering member of the Apiaceae family. My first thought at the time was Zizia (known as golden Alexander) but the more knowledgeable folks started a discussion about how it could be Thaspium (known as woodland meadow parsnip). I was new at the time and didn’t catch the finer points of the discussion but it was enough to stick in my mind that these could be confused.

Rescued plant

Last year I rescued a plant in the winter that looked like something in the Apiaceae family. I love getting new native host plants (Apiaceae family plants are hosts for the Eastern Black swallowtail butterfly), so I rescued it. Like my Zizia, it kept some foliage all winter. Picture at left blooming in 2021.

I planted it in a sunny moist area (I found it in a moist area) and this year the flowers were spectacular. My already established Zizia aurea was a bit later to flower, but when it did, I now had some comparisons to make and off I went to find the identification points to help me. The leaves were past the basal growth phase but I found some points about the flowers and the seeds.

An umbellet (Zizia)

I like to use Weakley’s Flora of the Southeastern US (yes it is big but the “find” function – CTRL F on a PC – works quite well) and was very surprised to find these plants in multiple Apiaceae keys with clues for using flowers as well as fruit (and the key acknowledges it is hard to separate these without having the fruit). An important point here is whether the central flower (or fruit) of each umbellet (see photo) has a pedicel (a stalk).

According to the keys, the central flower on Zizia does not have a pedicel while on Thaspium, the central flower does have one. Here are photos from my plants. I had to cut away some of the flowers to show the center more clearly. The rescued plant has all flowers on pedicels while the known Zizia shows a short flower at center.

Mystery showing central flower

Zizia showing central flower

In addition to having the two yellow blooming plants, I also have a purple-flowering plant that is definitely Thaspium trifoliatum var. trifoliatum so that has been helpful to use as well in evaluating presence of a stalk on the central flower. Here are pictures of the plants in my yard now gone to seed. The mystery and the purple Thaspium are showing seeds on elongated stalks (pedicel) while the Zizia has that noticeably short one in the center.

Yellow mystery

Zizia

Purple Thaspium

Note that the seeds of the mystery flower are ribbed which is one of the points mentioned in the key for Zizia (see below) so that compounds the mystery a bit. [Although my Zizia's seeds aren't as ribbed.] Apparently I should have looked more closely at the mystery flower to see if the central flower was staminate as it is valid for Zizia to have a pedicel on the central flower when it is also staminate (having stamens).

So I guess the mystery may last another year until it blooms again and I can check that central flower more closely. None of my pictures from this year is clear enough to tell now. I do hope my exercise here will help some other folks regarding these two plants.

Note for those curious about the name golden Alexander: Zizia aurea was first classified as Smyrnium aureum but was changed in 1825. The common name is believed to refer to an old herb from Roman times called Alexanders (Smyrnium olusatrum) and named for the city of Alexandria.

Here are snippets of two of the keys from Weakley’s Flora of the Southeastern US: