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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Monday - October 06, 2014

From: charleston, WV
Region: Mid-Atlantic
Topic: Seeds and Seeding, Wildflowers
Title: Silphium Perfoliatum Seeds
Answered by: Anne Van Nest

QUESTION:

I am trying to identify which part of the seedhead is the actual seed of the cup plant, Silphium perfoliatum. It is hard to find images. Some show the outer, larger, flat part of the seedhead which I thought was the husk. I always thought the seeds were contained inside that, but still visible when looking at the top of the seed head. There are lots of very thin/skinny parts inside the flatter parts. I can send a photo if needed, but was hoping you might have a photo showing which of the two is the actual seed. Hope I've described this well enough!

ANSWER:

Silphium perfoliatum, the cup plant is a dramatic perennial that grows up to 9 feet tall with yellow aster flowers during July – September. Each flower has 20-30 yellow ray petals and a darker yellow disk. Coarse foliage clasps the stem without a petiole and the small cup that is formed actually holds water. This feature attracts birds to the plant.

The plant is native to an extensive region from Southern Ontario to North Carolina and west to the Great Plains.

The deep roots make it difficult to transplant the cup plant, but it is easily propagated by seed. Collect the seed in September and October. Sow the unstratified seed in spring or stratify the seed (3 months of cold and moist treatment in the refrigerator) and sow it in the fall. Apparently goldfinches descend up the plant and devour the seeds.

The Illinois Wildflowers website has some additional information about the seeds. Each sunflower-like composite flower is about 3-4" across, consisting of numerous yellow disk florets that are surrounded by 18-40 yellow or pale yellow ray florets. The infertile disk florets protrude somewhat from the center and are rather conspicuous, while the ray florets are fertile. The latter produce thin achenes, each with a well-developed marginal wing, which are dispersed to some extent by the wind.

According to www.hort.net The fruit is a brown obovate achene with an emarginate apex, appearing in autumn. Sometimes 2-toothed.

Prairie Moon Nursery has a picture on the seeds on their website which shows the 2-toothed heart-shaped nature of some of them.

The Go Botany website has images and info from the New England Wild Flower Society and has an excellent slide show that has exactly what you need to see how and where the seeds are formed.

And finally, the USDA has a great closeup image of the Silphium perfoliatum seeds on their Plants Database website.

 

From the Image Gallery


Cup plant
Silphium perfoliatum

Cup plant
Silphium perfoliatum

Cup plant
Silphium perfoliatum

Cup plant
Silphium perfoliatum

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