Monday, September 28, 2015

The fatal flowers of Tall Thistle (Cirsium altissimum)

Tall Thistle (Cirsium altissimum); Durham Co, NC (9/14/15)

I find Tall Thistle (Cirsium altissimum) to be one of our most interesting natives.  Perhaps this is because I often root for the underdog, and so many gardeners, farmers, and even "conservationists" despise thistles. Hopefully their aversion may change if they come to understand the wildlife uses of native thistles and more particularly the benefits for native bees and butterflies. A fairly impressive, preliminary list of these has been documented using Tall Thistle, including over 20 native bees and nearly as many butterflies (1)

Hummingbird Clearwing Moth (Hemaris thysbe) visiting Tall Thistle; Durham Co, NC (9/14/15)

Tall Thistle occurs widely across the eastern US, from the prairie regions eastward, but is largely absent from the southeastern coastal plain. In North Carolina it has been reported mainly from western Piedmont and mountain counties; Durham County appears to be the easternmost location in the state.

Predominately white flowering Cirsium altissimum with a scattering of pink flowers  (Durham Co, NC - 9/14/15)

The majority of plants I have seen in North Carolina flower white, with a lesser intermixing of pink flowers (elsewhere in the range flowers seem to be more typically pink or purple and less commonly white). Tall Thistle is "monocarpic" meaning individual plants die shortly after flowering and setting seed (the classic case of monocarpism is the Century Plant). Cirsium altissimum is sometimes listed as biennial, but one group of authors (2) documented individual plants taking up to 4 years to emerge from young rosettes (such as the one shown below) into flowering stems.

Densely pubescent leaves of C. altissimum

In comparison to most thistle species, Cirsium altissimum has relatively soft and prickle-free leaves. Lower leaf surfaces are covered with dense white pubescence and stems are obviously hairy to the naked eye. Large leaves, a foot or more long, may develop on heavily shaded plants (see below). Some flowering stems exceed 10' in height and most produce multiple blooms.

Large shade leaves of C. altissimum, almost free of thorns

The large natural range of Tall Thistle and frequent occurrence in many regions suggest this is not, generally, a species whose survival we would need to be overly concerned about. HOWEVER, in a strange twist of fate, Tall Thistle may now be threatened by efforts in Midwestern prairie regions to eliminate truly problematic and invasive thistle species. A "bio-control" agent (weevil) deliberately introduced to control non-native thistles actually uses Tall Thistle "as frequently and intensively as it uses the targeted, exotic host plant" (3).

Cirsium altissimum seems to thrive only in relatively open habitats.  Ironically, the site where Tall Thistle occurs in Durham Co, NC also happens to be both nutrient rich and moist, creating growing conditions very conducive to dense woody plant growth. This apparent conundrum seems to suggest, at least in our area, that Tall Thistle requires regular disturbance and is likely another in the growing list of fire benefiting species. In fact, the currently large Durham population only appeared after burning. Thus far, we have been able to keep a portion of the site open with a combination of prescribed fire, selective chainsaw removal of trees, and invasive plant control.

Tall Thistle (Cirsium altissimum) flowering in open, "savanna"; Durham Co, NC (9/25/15)


Saturday, September 26, 2015

Mountain Bog Recovery & Expansion

Bog edge, before thinning (June 2015)
Bog edge, after thinning (July 2015)

The above images were taken near the perimeter of a so-called "mountain bog" in western North Carolina.  The first image shows the conditions before active restoration, the second image shows the same locale after clearing dense rhododendron invasion.  The only evident trees in the initial image are red maple and a lone pitch pine (Pinus rigida). After clearing the dense brush, a number of previously hidden stems of Pitch Pine in the heart of the wetland become apparent. The images also document (especially the second one) a small tributary creek feeding into the site from a black plastic culvert. Hugging the margin of this tributary (just past the lone pitch pine) is a grove of pitcher plants (see image below). 

Numerous pitcher plants (Sarracenia jonesii) hiding in this dense herbaceous foliage
At one time other rare plants were apparently present here when the creek was able to fan out gradually across the area, and the site was more open. However, years ago a road was constructed through the edge of the wetland. Several feet of fill material buried portions of the wetland, and altered the hydrology in some subtle and not so subtle ways (plans are in the works to remove the offending road section and culvert in hopes of restoring more natural water flows and reopening original wetland surface area for bog plants, stay tuned!). The dense thicket of shrubs that developed along the altered stream course excluded nearly all ground layer plant diversity directly underneath. In addition, the thick wall of green created both a sun and rain shadow across the nearby pitcher plants (these pitchers thrive in open sun, in saturated soils).   

Bog edge, before Rhododendron removal (June 2015)
Bog edge, after Rhododendron removal (July 2015) 

Numerous studies have shown that canopy vegetation can intercept and effectively remove up to 50% of seasonal or annual rainfall (Carlyle-Moses and Gash 2011, Forest Hydrology and Biochemistry). In contrast to deciduous plants, the evergreen rhododendrons continue to intercept rainfall all year long. At this site, the result could be losses of as much as 30" of water recharge per year! By removing the wall of rhododendrons we hope to create more open, sunlit conditions and add water back into the wetland system.  

Pile of Rhododendron previously removed from interior and margins of bog

We have been working on this restoration for several years, having been slowed mainly by lack of funding and resources to complete the task; the Friends of Plant Conservation ( has recently established a means by which people can support this effort. 

Mountain Bog interior conditions in 2011, before restoration, note forked pine tree

Mountain bog conditions in 2014 after interior brush removal, note forked pine
Elsewhere on this blog I have discussed a few of the rare plants whose populations have begun to rebound due, in part, to these restoration efforts.  Won't you help this progress continue?

Saturday, September 12, 2015


American Bluehearts (Buchnera americana) @ Taberville Prairie, Missouri (8-19-15)
I came across a few individuals of American Bluehearts (Buchnera americana) during recent explorations of the tallgrass prairie. According to Bruce Sorrie and Alan Weakley I was in the "heart of the range" for the species. Back home in North Carolina American Bluehearts is considered an endangered species and is believed to have been lost from nearly every location from which it has been documented. This made finding a few plants feel even more special even if they aren't so rare out in Missouri.  

Savanna Bluehearts (Buchnera floridana); Boiling Spring Lakes Plant Conservation Preserve, Brunswick Co, North Carolina (6-03-15)

Bluehearts was perhaps first documented in Carolina by Reverend Moses Ashley Curtis. In his "Catalogue of the Indigenous and Naturalized Plants of the State" (published in 1867 at the "N.C. Institution for the Deaf, and Dumb and the Blind"), Curtis provided no clues about the abundance of American Bluehearts but listed it only in the "Mid. and Up. Districts", regions most often referred to as the Piedmont and Mountains today. We now recognize an additional Buchnera species found in the coastal plain region as well, Savanna Bluehearts (Buchnera floridana) (see image above).  In contrast with American Bluehearts, Savanna Bluehearts characteristically has fewer and more compact flowers (although taxonomic treatments by Bruce Sorrie emphasize leaf characters to distinguish the two). There are some indications that Savanna Bluehearts may be pretty rare in North Carolina (although comprehensive data are lacking since it is not currently tracked by our Heritage Program). 

Buchnera sp. perhaps intermediate in some characters between B. americana and B. floridana?
St. Marks NWR, Northern Florida (7-05-14)

Savanna Bluehearts don't seem to occur further north than North Carolina, but rather extend southward across parts of the southeastern coastal plain, and may not extend beyond the coastal plain. American Bluehearts is primarily centered in Kansas, Oklahoma, and Missouri with spotty occurrences elsewhere, including into the northeast and to the edge of Lake Huron.  The ranges of the two species may overlap, but the extent to which this happens, especially the mid-south and parts of the southeast, remain unclear (at least to me) (see image above). Part of the reason the distribution and status of both species is uncertain is due to the fact that the two names are considered synonymous in many areas. For example, NatureServe lumps them together and therefore believes the combined entity is perhaps globally secure.  However, American Bluehearts have apparently been extirpated from several states and are considered quite rare or vulnerable in a significant number of others. If the populations consisting of Savanna Bluehearts were seperated from the tally, both species could turn out to be important elements of conservation concern.  

American Bluehearts amidst dense grass cover in tallgrass prairie remnant @ Taberville Prairie, Missouri

In the so-called heart of the American Bluehearts range, where I observed it, the species was found in "tallgrass prairie". Today, there are mere remnants of this once vast ecosystem that the US Fish & Wildlife Service ( believes has become "functionally non-existent over the last 150 years".   In my recent forays in Missouri prairies, I encountered American Bluehearts only in 2/20 + remnants visited and found < 5 individuals at each (although my observations were not systematic or comprehensive).  Savanna Bluehearts seems to have occupied longleaf pine savannas which could be considered ecologically analagous to tallgrass prairie, and has suffered a similar fate. Importantly both habitats were once subject to frequently recurring fires that likely benefit both Buchnera species.  A large part of the conservation challenge ahead will be to ensure that sufficient high-quality habitat remnants of both ecosystem are protected from ongoing threats and are adequately fire managed.   

Sunday, September 6, 2015

Tallgrass Vignettes

Standing amidst this sward of tallgrass prairie in Southern Kansas one evening (08-22-15) brought this line from Willa Cather to mind: ".......I felt the grass was the country, as the water was the sea."

Sweet Coneflowers (Rudbeckia subtomentosa) @ Osage Prairie, Missouri (8-19-15)
Profusion of Flowering Spurge @ Linden's Prairie, Missouri (8-20-15)

A few stalks of flowering Big Bluestem (Andropogon gerardii) stand above patches of Flowering Spurge (Euphorbia corollata) and a few other species @ Paintbrush Prairie, MO (8-16-15)

Stiff Sunflower (Helianthus pauciflorus) patch @ Tallgrass Preserve, Kansas (8-16-15)

Big Bluestem flowering above Flowering Spurge, Rosinweed stem on the left @ Tallgrass Preserve, Kansas (8-16-15)
Ashy Sunflowers (Helianthus mollis) @ Paintbrush Prairie, Missouri (8-17-15)

Flowering assemblage with Blue Sage (Salvia azurea), Ironweed, and Goldenrods @ Taberville Prairie, Missouri (8-18-15)

Getting on to evening at Golden Prairie, Missouri (8-22-15)