Oh Dread! Another Naturalized Exotic Plant?

Driving down the highway along the Northeast Cape Fear River near Wilmington recently, I caught a glimpse of the plants shown above.  The 5-6' tall plants with bright yellow flowers were unfamiliar so I risked life and limb and pulled a U-turn on the heavily traveled road to take a closer look.

Ludwigia bonariensis, near Eagle Island, NC
July 7, 2014

The plants were incredibly attractive and intriguing.  I concluded they were most likely Ludwigia bonariensis.  I was excited by the comment in the Manual of Vascular Flora of the Carolinas which listed it as "very local; Brunswick and New Hanover cos." --- this thing was rare!

But then I got confused!

A later check of Godfrey & Wooten (Aquatic & Wetland Plants of the Southeastern United States) listed it as  "Local, s.e. N.C.; Fla." but added, "native of Trop. Am." --- this thing was exotic!

Weakley's Flora stated it is "apparently native of tropical America" and suggested it may have been introduced on ship's ballast, while noting our plants appear to differ somewhat from specimens elsewhere.

NatureServe considers it exotic in NC, SC, and AL, but lists it as "critically imperiled" in Arkansas. Also of interest is the common name used by NatureServe; "Carolina Seedbox" - an odd name for something from the tropics.

USDA Plants lists it as native in NC, SC, AL, and FL and doesn't record it all from Arkansas.

Both USDA Plants and NatureServe omit the record that showed up in an artificially created wetland in VA around 10 years ago....

My head is humming and it won't go - in case you don't know.....

Ludwigia bonariensis sepals and capsules, just west of Wilmington, NC

IF ANYONE CAN SHED LIGHT ON EITHER THE TAXONOMY OR NATIVE DISTRIBUTION OF THIS SPECIES IT WOULD BE APPRECIATED!

Piedmont Savanna Restoration @ Hebron Road

STAR indicates Preserve location,
ARROWS point to surrounding "urban interface"

                                                        The Hebron Road Plant Conservation Preserve, in the Piedmont of North Carolina, is actively managed with the goal of restoring open, savanna-like habitats and a naturally-occurring suite of rare plants. At this site in particular this goal poses many management challenges.  The site is ringed by development including well traveled roads, an elementary school, and a massive subdivision. All these factors make prescribed burning difficult.  

Evening prescribed Burn conducted March 29, 2012

North Carolina has smoke management guidelines that must be followed when conducting prescribed burns.  Our site has a very narrow set of conditions under which it can be burned, meaning only a few days are available each year.  In order to capitalize on one of these infrequent events, in 2012 we burned at dusk, with direct input from the National Weather Service.

4/10/2015 after most recent prescribed fire.
Redbud (Cercis canadensis) and Dogwood (Cornus florida) flowering in background
Brown unburned patches are mostly Indiangrass (Sorghatrum nutans)

The site was burn again in Spring 2015 (regular fires are needed to control woody plant growth, encourage flowering of rare perennials, create seedbeds for germination, etc).  Like many other "growing season" burns, the fire did not consume the undergrowth entirely across the the site.  The most open, grassy areas burned less completely than those where hardwood leaf litter predominated.

Last year's growth of Smooth Coneflower (Echinacea laevigata) stands tall in one of the unburned patches (4/10/15)

4/19/2015 regrowth of Ironweed (Vernonia sp) after prescribed fire. 

The Preserve was established to protect a remnant population of the federally endangered Smooth Coneflower (Echinacea laevigata). When acquired, all the Coneflower stems were found along the roadside.  Slowly, but surely the population continues to expand at the site. Importantly many of the current plants are now found further away from the roadside and the threats that come with it.


 (left): Vigorous patch of Smooth Coneflowers (06/11/14) established from seed collected on-site. Boulders of diabase rock are present.

E. laevigata seedling sprouting after fire (04/07/15)

Narrow-leaf Aster (Symphyotrichum laeve var. concinnum)
seedling sprouting after fire (4/07/15)

Several other rare plants found on the Preserve also appear to benefit from the restoration and management activities. The Narrow-leaf Aster (Symphyotrichum laeve var. concinnum), listed as Threatened in North Carolina and known from only a handful of sites in the Piedmont, is expanding. 

Narrow-leaf Aster (Symphyotrichum laeve var. concinnum)
Fall flowering, Durham Co, NC (10/10/11) 

Erect Bindweed (Calystegia spithamea)
Spring flowering, Durham Co, NC (05/14/15)

Erect Bindweed (Calystegia spithamea), considered a "watch list" species in NC, occurs at the Preserve at what appears to be the easternmost location documented in North Carolina.  This low growing species doesn't appear to compete well as vegetation becomes taller and more robust in the absence of fire. Another rare plant found on the site, Prairie Dock (Silphium terebinthinaceum), also reaches its approximate eastern occurrence in North Carolina here and thrives with fire. I previously discussed this species http://ncplantcon.blogspot.com/2014/08/prairie-flora-in-north-carolina-all.html

Prairie Dock sprouting after spring fire@ Hebron Road Preserve

Prairie Dock flowering @ Hebron Road Plant Conservation Preserve
Fall Flowering (8/23/14)

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.