Another Day, Another Sandhill

Target Species: Centerville Brazos Mint (Brazoria truncata var. pulcherrima)

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Centerville Brazos Mint blooms among other rare plants in a high quality xeric sandhill

My pursuit of the Centerville Brazos Mint (Brazoria truncata var. pulcherrima brought me back to the xeric sandhills, the interesting community where I recently photographed the Smooth Jewelflower.  This time, instead of heading southeast to the Big Thicket, I traveled northeast to the transition zone between the Pineywoods and the Post Oak Savannah.  Here I found a community described by Texas Parks and Wildlife as “East-Central Texas Plains Xeric Sandyland.”

The Centerville Brazos Mint is rare.  The entirety of its range is confined to Texas, and it requires very specific conditions – deep sands with an open overstory.  These communities have declined dramatically since the colonization of Texas, and today very few high quality examples remain.  Fortunately I was able to visit some that likely appear as they did before Texas was settled.  Though they may be rare, where they occur, the Centerville Brazos Mint often thrives, forming carpets of pink over the sand.

Brazoria truncata var. pulcherrima is a member of the mint family (Lamiaceae) that is restricted to a handful of counties in East-Central Texas.  The genus Brazoria is named for the Brazos River, where it was first collected.  There are three species, all of which are endemic to Texas.

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Centerville Brazos Mint

Where the Centerville Brazos Mint grows, other good things are sure to be found.  A suite of rare species occur in these sandhills.  Studies of these communities have found that they contain one of the highest levels of endemism in the Western Gulf Coastal Plain.  The day I visited I found another rare Texas endemic mint blooming in profusion – the Texas Sandmint (Rhododon ciliatus).

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Texas Sandmint

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Texas Sandmint

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Texas Sandmint

I arrived early, and spent most of the day exploring the sandhills.  At around 4:30 pm I began to see flashes of deep pink.  I recognized them as the blooms of the Prairie Fameflower (Phemeranthus rugospermus).  Another rare species, it occurs in the Central U.S. from Minnesota to East-Central Texas.  It has succulent leaves, an adaptation for the drought-like conditions that occur in the deep sands that it prefers.

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Prairie Fameflower

The Prairie Fameflower is so rare that it was once considered for listing under the Endangered Species Act.  It remains endangered on many state lists.  Most of the flowers I saw were a brilliant deep pink.

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Prairie Fameflower

There were a few, however, that were a light, faded pink.  The flowers of Phemeranthus rugospermus open in the late afternoon, and only for a single day.

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Prairie Fameflower

Portions of the sandhill were carpeted by the low, creeping forbs Yellow Stonecrop (Sedum nuttallianum) and Drummond’s Nailwort (Paronychia drummondii).  In some areas the two were growing together.

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Yellow Stonecrop

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Drummond’s Nailwort

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Yellow Stonecrop

I also saw several Smooth Jewelflowers (Streptanthus hyacinthoides) in bloom.

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Smooth Jewelflower

Prickly Pears were abundant in the deep sands.  The individuals here key to Opuntia cespitosa per the new treatment of the Opuntia humifusa complex by Majure, et al.

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Prickly Pear

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Prickly Pear

These sandhills occur in isolated pockets within a broader band of Post Oak Savannah uplands.  These savannahs were beautiful and diverse in their own right.  Though I didn’t have time to explore them properly during this visit, it gives me something to look forward to on my next visit.

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Butterfly Weed (Asclepias tuberosa) blooms in a Post Oak Savannah

 

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Jewel of the Sandhills

Target Species: Smooth Jewelflower (Streptanthus hyacinthoides)

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Smooth Jewelflower

I have long admired the bizarre blooms of the Smooth Jewelflower, but had not previously sought it out.  Though it may be locally abundant, Streptanthus hyacinthoides is uncommon to rare in Texas.  A species of deep sands, it is most frequently encountered in the northern reaches of the Post Oak Savannah.  Globally it occurs from extreme southern Kansas and central Oklahoma through northeast Texas into northwestern Louisiana.  There are also a couple of disjunct populations in the Pineywoods: in the Big Thicket in Hardin and Newton Counties.

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Smooth Jewelflower

It was here that I sought them out.  In the Pineywoods they occur in xeric sandhills.  In the literature, these unique communities are variably referred to as xeric sandhills, oak-farkleberry sandylands, xeric sandylands, sandhill pine forests, etc.  Here soil conditions inhibit the growth of many species.  The deep, coarse sands here ensure that even in times of high rainfall, the water percolates down through the soil very rapidly.  As a result, xeric sandhills exist with perpetual drought-like conditions, and only drought-adapted species persist.

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Smooth Jewelflower

I was able to locate this population thanks to the help of my botanist friend Eric Keith, and Wendy Ledbetter, the Forest Program Manager of the Nature Conservancy in Texas.  Like so many more of our imperiled species, these rare jewels are protected by the Nature Conservancy.  I found them growing in a series of sandy clearings in a xeric sandhill dominated by Longleaf Pine (Pinus palustris) and Bluejack Oak (Quercus incana).

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Smooth Jewelflower

I found the strange flowers somewhat difficult to capture.  I found them strikingly beautiful in their uniqueness.  Beyond habitat preference, I could find little on the life history of this species while researching my 2017 list.  It seems that there is still much to learn about this peculiar jewel of the sandhills.

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Smooth Jewelflower

Xeric sandhills are also home to a variety of other unique and beautiful flowering plants.  Cacti and yucca, typically considered genera of the southwestern states, thrive here.  Traditionally the cactus species of this region was considered to be Opuntia humifusa, however recent work by Majure, et. al. is challenging that (More on that in a later blog post).  Using their new dichotomous key I keyed this species to Opuntia mesacantha.

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Opuntia cf. humifusa

The beautiful Carolina Larkspur (Delphinium carolinianum) was also blooming in profusion.  I photographed the individual below from different angles, to see how the angle of light changed affected their color.

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Carolina Larkspur

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Carolina Larkspur

We also found the bizarre Large Clammyweed (Polanisia erosa) nearby.  I have heard the blooms described as miniature moose heads.  Large Clammyweed, like many species of xeric sandhills, is endemic to the West Gulf Coastal Plain.

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Large Clammyweed

Butterfly Weed (Asclepias tuberosa) was also blooming in profusion.  This striking milkweed is common in sandy habitats throughout much of the United States.

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Butterfly Weed

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Butterfly Weed

Farkleberry (Vaccinium arboreum) is a conspicuous mid and understory component in xeric sandhills.  This blueberries produce edible fruits.  Though they are much smaller and less flavorful than what you might find in your grocery store, they still make for a refreshing treat while wandering across the parched sand.

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Farkleberry

Growing tangled among some of the numerous Farkleberries we found the twining stems of the Netleaf Leather Flower (Clematis reticulatus).

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Netleaf Leather Flower

Xeric sandhills are certainly one of my favorite places to explore.  This post barely scratched the surface of the diverse flora that occurs here, and I didn’t even mention the many rare and interesting animal species that can be found in these deep sands, and I hope to revisit these special places in future blog posts.

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Cacti bloom in a xeric sandhill