Purple (Not really) Bitter Cress (Cardamine douglassii)

Cardamine douglassii (04/08/15)
Durham Co., NC

Cardamine douglassii is sometimes called Limestone Bitter Cress, or Purple Bitter Cress. Neither name seems to be that appropriate (but common names rarely are),  First, it only rarely (maybe never?) grows directly on exposed limestone, and certainly never does so in NC. Second, the flowers are rarely purple, but nearly always appear pure white (but see below). For these provincial reasons, I prefer to call it "Douglas's Bitter Cress".

Douglas's Bitter Cress,
atypical "purple flower" variant
Granville Co., NC

Douglas's Bittercress is another plant species with restricted distribution in North Carolina, and which seems to be most abundant or widespread in the mid-western United States.  In North Carolina it occurs only in a few Piedmont counties, including Durham & Granville; these locations and the those in the Virginia Piedmont are significantly disjunct from the nearest populations to the west.  The habitat where I have observed the species is infrequently flooded floodplain forests. One of the sites supporting the species is shown below:

Cardamine douglassii habitat in Durham Co., North Carolina
Bottomland Hardwood Forest, lush cover of Spring Beauty (Claytonia virginica)
04/11/15, Cardamine just finished flowering

Like other Bitter Cress species, Cardamine douglassii is part of the Mustard or Brassicaceae family and produces slender tubular seed capsules, or "siliques", that are much longer than wide.

Cardamine douglassii in full fruit

Stems usually lack leaves for most of their length. Several accounts from other states indicate stems are hairy, but I have not observed that in North Carolina. Cauline leaves are usually found on the lower third of the stem, unlobed and usually toothed. Basal leaves are more heart shaped. Younger, non-flowering plants of these perennials produce only rounded leaves

Fortunately, the species seems to require little in the way of active management.  Localized threats to populations in North Carolina include construction & maintenance of water and sewer easements. installation of waterfowl impoundments, beaver flooding, and competition with invasive exotics, especially Japanese Honeysuckle. 

Plum Thicket Part 1, American Plum

American Plum flowering amidst Eastern Red Cedar, and open grassland
Durham Co., NC April 15, 2015

American Plum (Prunus americana) occurs in scattered localities across the North Carolina Piedmont & Mountains but is generally absent or infrequent in the coastal plain.  Wide ranging across North America, it may have been cultivated by some Native Americans (see Havard 1895 in Bulletin of Torrey Botanical Club)

Showy, white, highly aromatic flowers develop before the leaves, and before most other deciduous species have leafed out in our area.

American Plum thicket of dense sprouts
invading a frequently burned "prairie-like" habitat

Small American Plum tree

American Plum tree with drooping branches
Note the sparse vegetation underneath vs.
dense grass growth outside

American Plum is infamous for forming dense thickets in certain open habitats. These thickets are due, in part, to its propensity to root sprout.  In the example shown here, sprouts are 3-5' tall and leafed out more fully than nearby mature trees, but no flowers were produced. Most have developed 10' or more from the main trunk and appear to be "invading" the open area, with the shortest sprouts along the leading edge.






The origin of these sprouts appear to be large Prunus americana individuals with well developed, widely spreading, and drooping branches, above twisted,multi-trunked stems. These small trees (see images following) produce significant masses of flowers. Interestingly, the space around the trunk(s) is clear of sprouts and other woody plants, possibly due to the density of the canopy or the species may be allelopathic.

The following sequence illustrates progressive stem development.   

Prunus americana sprout elongating above surrounding stems
Note resemblance to brambles or rose canes (to which they are related) 

Prunus stem undergoing height & diameter growth,
developing vertical dimension, showing well developed spur shoots

Small diameter tree with splitting bark, few shoots emerging directly from trunk

American Plum with massive (for the species) triple trunk

Progression of American Plum sprouts to trees,
with small sprouts (left), small tree flowering (middle), large flowering tree (right)

Well-formed & floriferous American Plum
Durham County, April 08, 2015

American Bladdernut (Staphylea trifolia)

American Bladdernut is widely distributed across the eastern United States from approximately western New England across much of the midwest into eastern Minnesota. In the extreme southern US, it is less frequently encountered but is scattered across MS, AL, and into the Piedmont of the Carolinas.   The presence of dangling "bladders" make the small tree easy to recognize throughout the winter.

The so-called bladders are actually papery textured, three-chambered capsules enclosing one or more hard, stony seeds. I opened a handful of capsules, expecting one seed in each of the 3 chambers. However, most had only one seed per capsule, a couple had 2, and only a single pod had 3 seeds. With a much larger sample, Harris (1912), writing in Botanical Gazette, found that longer pods tended to produce more ovules or seeds.

Seeds are bright & shiny, and bead-like. Those of the European species, S. pinnata, were regularly and widely used in rosaries (Lukzaj 2009, Dendrologicznego). Celts planted them on graves and other significant sites, and fossil remains are often associated with Roman & Medieval archaeological sites, often outside of its perceived native range (see Latalowa 1994 in Vegetation History & Archaeobotany).

In North Carolina our species, Staphylea trifolia, is typically a "bottomland" or "riparian" species; the bladders are thought to aid seed dispersal . I dropped a handful in water and the image (left) confirms, they do indeed float!  Perhaps not surprising, most naked seeds sunk rapidly. 

Water dispersal may explain why most of the stems I have observed along the Eno River in Piedmont of NC, are close to, or even overhanging the river.  

Typical habit of American Bladdernut
Along Eno River, Durham Co, NC
Note multiple, whitish-gray trunks above River Oats (Chasmanthium latifolium)

Image below (near the "Pump Station" on Eno River)
This part of the river floods more regularly than the above site, consequently
shows more extensive damage presumably from flood debris (see ground nearby)

American Bladdernut has oppositely arranged twigs and buds. Reddish-brown buds are evident in the winter (below; Jan 25, 2015). 

 

In the North Carolina Piedmont, Bladdernut buds began bursting open on March 22, 2015 (see above). Soon, the trifoliate leaves will be fully developed as shown on the specimen below:

Sessile Trillium - a rare myrmecochore in North Carolina

Trillium sessile: red petalled form in northeastern NC

Sessile Trillium occurs on the southern periphery of its natural range in northeastern North Carolina near the Roanoke River.  In Carolina this Trillium is known from two counties and is considered "Threatened" in the state.  Most individuals seem to have red petals as shown on the image above, but some individuals (as shown below) have greenish-yellow petals, apparently due to diminished or absent anthocyanins (for more information see Les etal. 1989; American Journal of Botany). 

Trillium sessile: light color form
Image date: 04/09/14

Sessile Trillium is widespread and common in the Missouri Ozarks and parts of the midwestern US. It is much less widespread east of the Appalachians although it does range across much of the Virginia Piedmont and into the coastal plain.  How does a species considered a "myrmecochore" (adapted for ant dispersal) develop a range like this?

For an excellent chance to see this rare plant in North Carolina, consider joining the Friends of Plant Conservation on April 07, 2015.  

More information can be found here:

http://www.ncplantfriends.org/Pages/FieldTrips.aspx

Spring Bartonia; Coastal Plain Endemic

Bartonia verna flowers (03/11/15)

Spring Bartonia (Bartonia verna) is an unexpected member of the Gentian family that appears in early spring. One of the many species first discovered by Andre Michaux, populations are restricted, or endemic, to the outer coastal plain of the southeastern US. The northernmost range consists of a single population located near VA Beach (Belden etal. 2004, reported in Castanea). Over half of the states where it has been documented consider it to be rare, including North Carolina.  A couple of the other states (MS, AL) have not explicitly considered its rarity, but like surrounding states it is almost certainly very restricted in those areas; Florida is the only state where the species is widespread (http://plants.usda.gov/core/profile?symbol=Bave2)

Spring Bartonia habitat at a site in South Carolina (03/11/15);
Pond Cypress depression pond with extensive standing water at flowering time

Sorrie & Weakley 1999 consider Bartonia's range generally synonymous with longleaf pine. The local habitat often includes wetland margins such as the example shown above on the Francis Marion National Forest.  The flowering Bartonia individuals located at this site occurred adjacent to pitcher plants, especially the Hooded Pitcher (Sarracenia minor), and Peanut-Grass (Amphicarpum muhlenbergianum). 

Bartonia verna multi-floral stem just opening

Bartonia verna in several inches of standing water; amidst brown stems of  Peanut-Grass

All Bartonia species (we have 3 in our area) are similar in having reduced leaves and root characteristics which may suggest a dependence on mychorrizal relationships to gain nutrients. Although B. verna has not been studied, Cameron & Bolin (2010) found that Bartonia virginica plants were enriched in carbon and nitrogen relative to surrounding vegetation and suggest that species is at least partially mycoheterotropic.

Cabbage Time in Carolina!

Skunk Cabbage (Symplocarpus foetidus) is one of our earliest, native bloomers. In mid-February, I observed dozens, possibly hundreds, of individuals pushing up through leaf litter, muck, and shallow water at a site near Warrenton, NC.

The stout emerging stalks are amazingly thick and leathery to the touch. They unfurl at various rates to form leafy "spathes".  I observed incredible variation in the appearance and coloration of these, ranging from light green to heavily striped, to mottled, to almost solid dark red.




Skunk Cabbage is a member of the Araceae family, which includes mostly tropical species. In our area its closest relatives include Golden Club & Jack-in-the-Pulpit.  Symplocarpus foetidus is the only species of the genus in North America; Western Skunk Cabbage belongs to a different genus. Symplocarpus also includes some disjunct members in eastern Asia. It has been suggested the Asian and North American species of Symplocarpus have been isolated from one another for over 6,000,000 years (1).

Symplocarpus foetidus spathe; few plants observed had
developed this perfect oval shape
Warren County, NC (Feb 2015)

Skunk Cabbage open spathe revealing enclosed spadix,
Note the amount of water inside the spathe

Skunk Cabbage is famous for the ability to produce heat during early season flowering, a process sometimes called "thermogenesis". Indeed, S. foetidus is one of the most precise thermoregulators known, and is apparently able to maintain temperatures within ~ 3.5 ° C range, while ambient temperatures range over 37.5 ° C (2). Exactly what value thermogenesis conveys to the plant, if any, is unclear. Some believe it is an evolutionary hold-over present in a few primitive plant families.

According to Seymour & Blaylock (3), "there is no doubt that warming advances development and permits early flowering, but the adaptive value of this is obscure".

I observed several plants with groups of what appeared to be fruit flies buzzing around. Some authors have suggested the plant's thermogenic qualities provide a more attractive site for early season insects like these. Grimaldi & Jaenike (4) found that Skunk Cabbage is "a major breeding site" for one species of fly that "looks enough like Drosophila so that the casual observer might be confused" (5); I certainly wouldn't have known the difference! Whether these insects pollinate the flowers on the spadix is unclear.

Symplocarpus foetidus "ripe" & flowering spadix

The condition and maturity of the spadix and presence or absence of flowers was quite variable during my visit.  The following series of images shows a bit of this, as does the image above (with the dark brown spadix). However, very few spathes were open enough to easily reveal the contents. Even fewer were flowering, like the examples shown to the left. Several appeared to be just past and others much more so, while at least one spadix (below) seemed to still bedeveloping.

S. foetidus immature spadix

This ripening spadix was
lying in an open spathe,
like an Easter Egg waiting to be gathered

Bright yellow stamens exposed, zooming into these seems to show pollen that has
fallen onto the spadix surface 

North Carolina has the southernmost ranging populations of Skunk Cabbage is eastern North America. The species creeps into a few northern mountain counties in eastern Tennessee and western NC. Further east, there are 3 or 4 reported counties in the NC piedmont.  The site for these images is in Warren County, close to the Fall Line.  Although often considered a piedmont county, it sure felt like I was in the coastal plain.  The habitat was a non-alluvial wetland ranging from moist to mucky soils. Tulip Poplar & Red Maple were probably the dominant trees, but Black Gum and an occasional Pond Pine were present, Cane & White Bay Magnolia were common as well. Most of the plants were found in and around the muckiest and wettest area near the streamhead.

Skunk Cabbage habitat (Warren County); Feb 2015
most plants occurred above the standing water where a faintly developed "Y"
can be seen, just downstream a dense understory of cane develops

Skunk Cabbage habitat, same site as previous (April 2014)

References:
(1) Jun Wen, R.K. Jansen, and K. Kilgore. 1996. Evolution of the Eastern Asian and Eastern North American disjunct genus Symplocarpus (Araceae): Insights from chloroplast DNA restriction site data. Biochemical Systematics & Ecology 24: 735-747.
(2) Seymour, R. S. 2004.  Dynamics and precision of thermoregulatory responses of eastern Skunk Cabbage. Plant, Cell,& Environment. 27: 1014-1022.
(3) R. S. Seymour & A.J. Blaylock. 1999. Switching off the heater: influence of ambient temperature on thermoregulation by eastern skunk cabbage (Symplocarpus foetidus). Journal of Experimental Botany 50: 1525-1532.
(4) D. Grimaldi & J. Jaenike. 1983. The Diptera Breeding on Skunk Cabbage, Symplocarpus foetidus (Araceae). Journal of the New York Entomological Society 91: 83-89.
(5) H. D. Stalker, 1945; On the Biology and Genetics of Scaptomyza graminum Fallen (Diptera: Drosophilidae).

Crater the bay to restore it?

Carolina Bay wetland (1998);
the egg shaped, dark mass near the center of the image

Carolina Bays are enigmatic, isolated wetlands scattered across parts of the Atlantic Coastal Plain; enigmatic due, in part, to their characteristic northwest-southeast orientation, and ovoid shape, not to mention speculation as to their origin.

Whatever their ontogeny, most have been destroyed by ditching, draining, and other land-uses.  Many appear only as faint impressions on aerial images.





One reasonably intact example of a Carolina Bay is the object of our conservation & restoration efforts in Sampson Co, NC (shown on the image above). This bay persisted amidst a maze of logging roads and uplands managed intensively for timber production, unlike an adjacent example which was repeatedly logged and shows few remnants of its original wetland character. I have no explanation why this particular bay was spared. However, remnant vegetation persists, displaying characteristics of "cypress savanna".

Cypress Savanna (Sampson Co, NC)
with open canopy, multi-aged, scattered Pond Cypress (Taxodium ascendens),
Loblolly pines are also evident, inc; browned & dying trees in the background

The dominant trees throughout the wetland would likely have been Pond Cypress (Taxodium ascendens). Like the image above, there would have been a relatively open canopy, with few Loblolly pines (Pinus taeda), above a dense, herbaceous dominated ground layer. However, most of the bay is now closed canopied and dominated by Loblolly which invaded the wetland due to a combination of periodic droughts and very infrequent fire. 

Pond Cypress (left), loblolly pine (right)

Pines grow alongside cypress (see left), sometimes capitalizing on what appear to be raised mounds created by the Cypress. Because Cypress is both slower growing and more shade intolerant than loblolly, the predictable result is that pines will eventually replace the cypress.  They also absorb and transpire more water, drawing down the water table and further increasing their competitive advantage. 




Therefore, a primary restoration issue is removal of the pines. 

Given the sensitivity of the site, conventional logging was not an option, and felling individual trees was deemed too labor intensive. After extensive consideration and experimentation, we decided to bring fire back to the bay and implemented a prescribed burn in the middle of November.  

Loblolly pine overtopping pond cypress

Fire weather forecasting called for northeast winds @ 9 mph, 55 degrees, 44% humidity. Keetch-Byram drought index (KBDI) was high (over 500), and fuel moisture across all size classes was less than 20%. The fire carried well across the entire site, as expected.  Flame lengths stayed generally low although there was significant variation as measured by scorch heights afterwards. Active fire burned out quickly and was easily contained.  Dry fuel conditions allowed fire to smolder pockets of surface organic buildup consisting mainly of intertwined pine roots.  

Post Fire Conditions in Carolina Bay after November fire

Top: small pocket burned several inches deeper than surrounding, 

Middle: Red Maple roots exposed, heavily injured & toppled

Bottom: consistent surface organic reduction, some root exposure 

As a result, a number of trees throughout the bay succumbed. A few, like the Red Maple (Acer rubrum) shown above fell over and died immediately, while most trees either survived or died more slowly. The following chart displays the survival of the three most common trees, Loblolly Pine ("Pinus"), Cypress ("Taxodium"), and Maple ("Acer") across 5 diameter size ranges.  For a given species the colored lines within each size class show the number of stems before fire ("Pre") and the number surviving after ("Post"). 

These data show relatively heavy stem losses of Pines (blue lines) across all size classes, while mortality of Cypress (red lines) was concentrated in the two smaller size classes. Taken together, this shows an overall shift away from the strongly pine-dominated vegetation of the Carolina Bay before fire to an equal mixture of pine & cypress after fire.  The lone fire was not sufficient to restore cypress savanna but it produced significant progress.

Growing season conditions following November fire;
Pond Cypress tree stands amidst several dead loblolly pines,
and above a living red maple