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Friday, September 2, 2011

The St. John's-Worts: Under-Rated Landscape Plants


A St. John's-wort shrub planted itself in front of the palmettos, but which Hypericum is it?
 We have several species of St. John's-wort that have planted themselves on our property from groundcovers in our lawn to this shrub with its small yellow flowers, gracefully arching stems and reddish peeling bark. Recently, I decided that it was time to identify which Hypericum it is. So I carefully observed the flowers:


4 petals in a flattened X-shape and
2 large sepals

Turning the flower upside-down, the 2 large sepals are
subtended by 2 narrow bracts
If you're serious about identifying Florida's plants, "Guide to the Vascular Plants of Florida" by Richard Wunderlin and Bruce Hansen, is THE authoritative text. These plant taxonomists are also the experts that provide data for the online Atlas of Florida's Vascular Plants, which we often cite as our authority for mapping which counties plants occur and when identifying whether a plant is native or not.

Here is their list of Hypericum for Florida. Without the book, you could link to all 31 of the species, look at the photos, and try to decide, but the photos may or may not provide enough detail to correctly ID the plant. The book and its keys make the job of figuring out the species or subspecies more certain.


Here is the key in the Wunderlin and Hansen book where I knew I could figure out our shrub.

A good key provides a series of clear either/or choices.

#1 is easy to figure out the number of petals and sepals. There are obviously 4 petals, but I only saw two sepals without my magnifying glass, but still I had to choose the first #1 with 4 petals--not 5.

#2: Styles 2 or styles 3 or 4. I can see that there are 2 styles, so I pick the first #2.

#3: The pedicels (flower stems) are short the the 2 bracts are right under the sepals (calyx). So my shrub is Hypericum hypericoides or St. Andrew's cross. When I look it up on the online plant Atlas, the range covers the whole state and the photos match my shrub perfectly. So now I know what to call my beautiful shrubs.

Flower diagram from wiki-commons
In order to successfully use a key, you'll need to learn (or re-learn) the parts of the flower and some other botantical terms. But once you get started, it's rewarding to know exactly what you have.


When you purchase "Guide to the Vascular Plants of Florida" or any of the other books listed in the right-hand column, by clicking our links, FNPS earns a small amount of money. Thanks for your support.

Ginny Stibolt

4 comments:

  1. It IS useful to know exactly what you have, so you know how to deal with it... Thanks for the simple explanation of keys.

    V. Avery

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  2. I have too many hypericum in so many species to count. Love the cheerful yellow heads appearing out of nowhere.

    Use caution in using the Atlas maps as an authority for what counties plants appear in. The maps account for only VOUCHERED specimens and I can attest to Osceola County plants being severly under-represented as I live adjacent to natural conservation areas and many of the plants found aren't listed for our county.

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  3. Readers should note that there is now a third edition of the Guide to the Vascular Plants of Florida. This edition is more comprises species previously unvouchered previous editions, and has updated plant keys. The link in your article goes to the second edition.

    ReplyDelete
  4. Thanks for the heads up on the new edition. I've changed the link in the story and in the right hand column.
    Ginny

    ReplyDelete