Tuesday, January 27, 2015

Maryland Senna - A Savanna Species in North Carolina

Maryland Senna (Senna marilandica) is a plant I don't often think about in the dead of winter, and especially in moist, riparian forests, but I recently walked by a patch laden with pods near the Eno River.

Senna marilandica full of fruit approximately 100' from the Eno River
(January, 2015)

Plants are stout, herbaceous perennials, to 6' or so tall in our area. In late summer they produce some of the brightest blossoms around, both at the top and axils of the main stem.

Maryland Senna, full bloom
(Durham County, 8/19/2014)

An interesting evolutionary aspect of Maryland Senna is the presence of extrafloral nectaries (EFN) near the base of the compound-leaved petioles.  In general, these nectaries are sugar producing glands that offer nectar to ants, who in turn provide protection to the plant from herbivores.
Extrafloral nectaries (EFN)  are the dark tick-shaped objects shown above;
the one to the upper left is being visited by a black ant
(Granville County, NC 8/01/12)

Maryland Senna EFN with ant visitor (Durham County, 08/20/14)  
Brigitte Marazzi and co-authors, writing in the American Journal of Botany (2006), documented that Senna species with EFN have colonized a wider range of habitats and climates than species lacking EFN. They believe the "ant–plant protective mutualism" has a positive effect on plant fitness and may help to explain the greater species richness of the EFN bearing Senna, as well as the greater diversity of habitats they occupy.
Maryland Senna EFN with a different visitor (upper left)
Note the developing seed pod (right)
(Durham County, 08/20/14)  

Other than the odd occurrence of Maryland Senna near the Eno River (powerline cut along with Heliopsis helianthoides), I find it most often in open canopied, uplands associated with diabase soils. I sometimes refer to these as savannas (never having seen the plant in closed canopied forests on the same soils and geology). One of the sites for some of these images has been referred to as a "cedar glade."  In their study of Piedmont Prairie remnants, Davis and colleagues (Castanea 2002) indicate Senna marilandica has a "strong association with Piedmont Prairies" although they did not document it at any of the sampled prairie sites, only a power-line right of way. There are numerous references in other parts of eastern North America to this species being found in prairie-like habitats. I was lucky to see it, or closely related species, in a Bur Oak Savanna in northeastern Indiana, late this November (see image below), which is managed by prescribed burning. 

Maryland Senna in an open, diabase glade, Granville Co, NC
The uppermost stem is full of buds, near a developing compound leaf  

Sunday, January 11, 2015

Holy Moley!

Southern Star-nosed mole ((Condylura cristata parva)
Image location near Avery/Watauga Co line; Jan 02, 2015

While traipsing around in a high-elevation mountain bog over the recent holidays (certainly a great way to kick off the New Year) I encountered a true surprise!  Although I had never seen one before, I immediately recognized the critter shown above due to its distinctive fleshy appendage, sometimes referred to as a nasal star.  The unusual snout has been described as "a nose that looks like a hand and acts like an eye" and has been considered possibly the most sensitive touch organ among mammals (1). It turns out, the Star-Nosed Mole is characteristic of wetland habitats, such as the "mountain bog" where I encountered it, and unlike its relatives it remains active in the winter (both factors help to explain why I found the individual shown above). It also turns out that the star-nosed mole is a species of special concern in North Carolina (2), where they are often considered rare to uncommon, but sometimes locally abundant (3).  Star-nosed moles (Condylura cristata) range into Canada and the northeastern US. However, those restricted to the southern Appalachians have been considered a subspecies, Condylura cristata parva, the name I am applying here.

Habitat for the Southern Star-nosed mole in the northern mountains of North Carolina
Note: small stream channel on shallow, quartz gravel bordered by stunted & yellowing rhododendrons

Mountain bog habitats are an important conservation priority in NC and across the southern Appalachians. In North Carolina, a sizable number of imperiled plants occur in the small and isolated pockets of these wetlands that remain (although not all "mountain bogs" support rare or imperiled plants). Even though winter is not the best time for a plant survey, I did find a small clump of what I believe is Bog Clubmoss (Lycopodiella inundata). Here in NC this plant is considered significantly rare, being known from only a small handful (~ 3) wetlands in the mountains.

Compared to other NC mountain bogs I am much more familiar with, this site is higher elevation (> 4,600') and found in a less fragmented landscape. In addition, Sphagnum moss is more abundant than many other sites I have looked at. Hints of the high elevation come from the presence of Red Spruce (Picea rubens) and a couple of Ruffed Grouse I scared up. Cant't wait to visit this site again!
Red Spruce growing amidst Sphagnum Moss clumps in the wetland

(1) Catania, K. C. 1999. A nose that looks like a hand and acts like an eye: The unusual mechanosensory system of the star-nosed mole. Journal of Comparative Physiology
(2) http://www.ncwildlife.org/portals/0/Conserving/documents/protected_species.pdf
(3) Webster, W. D. 1987. in M. K. Clark, editor. Endangered, threatened, and rare fauna of North Carolina. Part 1. A reevaluation of the mammals. Occasional Papers of the North Carolina Biological Survey 3.