Tom's Blog

Monday, August 24, 2009

Varieties of sunflowers

The genus Helianthus is a taxonomic problem since many of the species are similar or hybridize. We have lots of sunflowers at Pleasant Valley Conservancy and I have been trying for the past few years to sort them out. Right now they are all flowering, which helps. The sunflowers are all clone formers, which means they form patches, sometimes large.

A few sunflower species are distinct enough that they can be classified with surety. Three that we have that fit in that category are sawtooth sunflower (H. grosseserratus), stiff sunflower (H. pauciflorus), and Jersualem artichoke (H. tuberosus, which is neither from Jerusalem nor an artichoke!). Sawtooth sunflower is found primarily in wet places, and we have it growing both in our marsh and (as a single patch, see photo at left) in the wetter part of the Valley Prairie.

Stiff sunflower is primarily a prairie species which is just becoming established at Pleasant Valley Conservancy. At present, there are two reasonably sized patches in the Pocket Prairie and a small patch below the prairie remnant along Pleasant Valley Road. This species is quite plentiful at the nearby Black Earth Rettenmund Prairie, and the photo here was taken at that site.

Jerusalem artichoke (Helianthus tuberosus) is a large-sized sunflower that forms extensive edible tubers. It is commonly found as large patches in marsh or wetland habitats, although it is also found in woodland areas. We do not consider this as a desirable species at Pleasant Valley Conservancy, and a large clone at the edge of our wetland was sprayed with glyphosate early in the spring. The bare area was eventually colonized with glade mallow (Napaea dioica), a State Threatened species. A small clone of Jerusalem artichoke still present along Pleasant Valley Road (see photo at left) will be monitored to ensure that it does not spread unduly.

In addition to the small clones of the above sunflowers, we also have a very large number of clones of woodland sunflower. There are several species of sunflowers for which the name "woodland" has been applied, including Helianthus divaricatus, decapetalus, and strumosus. Although H. divaricatus is widespread at Pleasant Valley Conservancy, there have only been a few collections made in Wisconsin, including the one that we made from Pleasant Valley Conservancy. I assume that this species is actually more widespread in Wisconsin than the data suggest but for some reason has not been extensively collected.

The main characteristics of H. divaricatus that separate it from the other sunflowers are: stems without hairs except near the inflorescence, lanceolate leaves, leaves opposite even near the flowers, and petiole small or absent.

A survey in August 2009, when the sunflowers were at peak flowering, located at least 95 clones of H. divaricatus, varying in size from six feet to 50 feet in diameter (perhaps larger). The photo below shows a typical clone.


Post a Comment

Subscribe to Post Comments [Atom]

<< Home