Jumat, 01 November 2013

Triadenum virginicum

Time to start catching up on photos from this growing season.
Back in late July, Lindsay and I joined a group from Save the Dunes on a quick trip to Pinhook Bog in LaPorte County, Indiana.  Led by staff from Indiana Dunes National Lakeshore, the walk down the boardwalk and back was very brief and only touched on the unique bog flora, but I used a free second to take a couple of photographs of a plant that I admire but don't see very often, Triadenum virginicum (Virginia Marsh St. John's Wort).
Triadenum virginicum in Pinhook Bog.
The most concentrated area of the geographical range of Triadenum virginicum is the New England region of the United States (and north into Canada).  The range of the species follows the Atlantic Coast south, around Florida, and along the coast of the Gulf of Mexico to Texas.  Like several other species with which it often grows, this modest pink-flowered plant is also disjunct in the Great Lakes region, making it a unique part of the flora in this part of the country.  Triadenum virginicum grows in bogs, interdunal swales, and wet meadows.

Note the pointed sepals and "long" styles of Triadenum virginicum.
A very similar species, Triadenum fraseri (Fraser's Marsh St. John's Wort), has a geographical range that overlaps with that of T. virginicum, but T. fraseri is found more in the Great Lakes and New England regions and north, without an affinity to the coastal plain.  It has been treated as a variety of T. virginicum in the past, but most botanists now consider the two to be distinct species.  The sepals of T. virginicum are longer (greater than or equal to 5 mm long versus up to 5 mm long in T. fraseri) and sharper pointed (acute to acuminate versus obtuse in T. fraseri), and the styles are longer in T. virginicum (more than 1.5 mm long versus less than 1.5 mm long in T. fraseri).  In addition, T. fraseri is rarely found with open flowers in the field (but they are said to open after spending an afternoon in a vasculum!), whereas it is not uncommon to see T. virginicum with open flowers.

Plants in the genus Triadenum were formerly treated as part of the genus Hypericum, but they are now distinguished from Hypericum due to petal and stamen characteristics.  The petals of Triadenum are pink or flesh-colored (versus yellow in Hypericum).  The stamens of Triadenum are in three groups of three and alternate with three large orange glands (versus being of various number and lacking glands in the flowers of Hypericum).  This unique characteristic of the flowers of plants in the genus Triadenum is the origin of their Latin name, as Triadenum means "three glands."

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