Friday Flower – Dwarf Spiderwort

Living at the foothills of the Ozark Highlands, I sometimes forget how unique the biota of this ancient landscape truly is. More than 200 species of plants and animals are largely restricted to the region, with around 160 of these being true Ozark endemics found nowhere else on earth. The biodiversity of the region stems from the landform’s unusual geology, topography and hydrology, it’s ectotonal position within the North American continent, and its distinction as the only significantly elevated landform between the Appalachian and Rocky Mountains. Many Ozark endemics are found in the region’s abundant caves and sinkholes, formed by underground dissolution of its massive limestone/dolomite bedrocks. Others represent isolated populations of more typically northern plants and animals that found refuge here during the Pleistocene glacial advances. Still others evolved during periods of isolation when vast inland seas covered much of the continent’s interior.

Tradescantia longipes, known locally as dwarf spiderwort or wild crocus, is a particularly exquisite Ozark endemic found scattered in dry igneous woodlands of the Missouri’s St. Francois Mountains and Arkansas’ Ouachita Mountains. I first saw this species two years ago in May at Crane Lake in the heart of the St. Francois Mountains, and the plants shown here were seen this past April in the igneous woodlands of Sam Baker State Park at the southernmost extent of the St. Francois Mountains’ igneous exposures. The genus to which this plant belongs contains some much more widely distributed (though no less striking) members (e.g. T. ohioensis, which I featured in my first “Friday Flower” post). Tradescantia longipes flowers are similar to those of T. ohioensis, but the plant differs from most others in the genus by its short, squat habit of growth and strictly basal leaves.

One feature shared by T. longipes with all other members of the genus is the dense fringe of hairs arising from the stamen filaments.  I discussed these in my first Friday Flower post, noting that each of the 70-100 hairs per filament is composed of a chain of about 20 large, single cells – easily seen with low magnification. While their sensitivity to radiation and chemical mutagens has been recognized for many years (the hairs turn pink when exposed to radiation), less seems to be known about their natural function for the plant.  It is interesting to note, however, that the flowers of Tradescantia and related genera rely heavily on insects for pollination (primarily bees and bee flies), yet they do not produce nectar.  Faden (1992) has speculated that the stamen hairs might combine with floral scents and the nearly pollenless anthers to deceptively attract insects, provide footholds, retain pollen fall, and influence the pollen-collecting behavior of the insects.

Photo Details: Canon 50D (ISO 100, 1/250 sec, f/14-18), Canon 100mm macro lens, Canon MT-24EX flash (1/4 ratio) w/ Sto-Fen diffusers. Post-processing: levels, unsharp mask, minimal cropping.

REFERENCE:

Faden, R. B.  1992. Floral attraction and floral hairs in the Commelinaceae.  Annals of the Missouri Botanical Garden 79(1):46–52.

Copyright © Ted C. MacRae

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Friday flower

Photo details: Canon MP-E 65mm 1-5X macro lens on a Canon EOS 50D, ISO 100, 1/250 sec, f/16, MT-24EX flash 1/8 power through diffuser caps

Photo details: Canon MP-E 65mm 1-5X macro lens on a Canon EOS 50D, ISO 100, 1/250 sec, f/16, MT-24EX flash 1/8 power through diffuser caps

While photographing small Acmaeodera beetles on flowers of Tradescantia ohioensis at Packsaddle Wildlife Management Area, I thought I should take a photo of the flower itself.  Flowers of Tradescantia species, or spiderworts, are notable for their bright yellow anthers and filaments with numerous hairs. Each of the (usually) six stamens possesses around 70-100 hairs, which in turn are composed of a chain of about 20 large, single cells that are purple in color and contain a large, water-filled central vacuole. The cells can be seen easily with low magnification – click on the photo to see the larger version, with the individual cells that make up each hair clearly visible. I haven’t been able to ascertain the function of these hairs for the plant, but their usefulness in observing division in plant cells (the flowing cytoplasm and nucleus can be seen easily) and their sensitivity to radiation and chemical mutagens have been recognized for many years. The hairs turn pink when exposed to radiation, allowing them to be used as a sort of ‘natural’ Geiger counter.

Update: While writing this post, I sent an email to George Yatskeivych, botanist at the Missouri Botanical Garden and author of Steyermark’s Flora of Missouri (1999, 2006), asking if he knew the function of the filamental hairs.  After reading his response (below), I don’t feel quite so bad for not being able to determine the answer myself:

I don’t know that I have ever heard anyone express a particular use for the hairs on the filaments of Tradescantia species.  Sometimes, hairy filaments help to trap pollen from visiting insects in proximity to the stigma or act as nectar guides, but I do not think that anyone has determined such “uses” in Tradescantia.  There may not be a selective advantage to hairy filaments in the genus.

If any botanist happens to read this post and has some insight about this, a comment would be most appreciated.

REFERENCES:

Yatskievych, G. 1999. Steyermark’s Flora of Missouri, Volume 1. Missouri Department of Conservation, Jefferson City, 991 pp.

Yatskievych, G. 2006. Steyermark’s Flora of Missouri, Volume 2. The Missouri Botanical Garden Press, St. Louis, 1181 pp.

Copyright © Ted C. MacRae 2009

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Ozark Trail – Marble Creek Section

If you know wilderness in the way that you know love, you would be unwilling to let it go…. This is the story of our past and it will be the story of our future. – Terry Tempest Williams


During the past several years that Rich and I have been hiking the Ozark Trail, most of our hikes have taken place in the fall and winter months. From a hiker’s perspective, I really enjoy these off-season hikes – the foliage-free canopy affords unobstructed views of the terrain and vistas, the cool (even cold) temperatures are more comfortable under exertion (provided one has properly layered), and there are no mosquitos to swat, ticks to pick, or gnats to incessantly annoy. I also enjoy them as a naturalist, for the world is quiet and still, allowing me to focus on things I may not notice amidst the cacophany of life during the warmer months. By the end of winter, however, the biologist in me yearns to once again see bugs and flowers and the great interplay of life. Unfortunately, this makes something as simple as hiking from point A to point B rather difficult – too many distractions! Nevertheless, each spring Rich and I try to hike a small leg of the Ozark Trail before the crush of summer activities fills our calenders. Last week, we chose the Marble Creek Section, an orphan stretch (for the time being) in the rugged St. Francois Mountains that eventually will connect to the famed Taum Sauk Section. It would be our first return visit to the St. Francois Mountains since we first embarked on our goal to hike the entirety of the Ozark Trail.

The St. Francois Mountains are the geologic heart of the Ozark Highlands. Since their primordial birth 1.5 billion years ago, recurring cycles of erosion and deposition have worn them down and covered them up, only to see them reemerge once again as the younger rocks covering them were themselves stripped away. The Ozarks are an ancient landscape with ancient hills, and none are older than those of the St. Francois Mountains. It’s as if the Earth itself began in these mountains. We began our hike at Crane Lake, a clear, blue 100-acre lake built in the 1970s by the Youth Conservation Corps. The trail surrounding the lake was built in 1975 and is, in its own right, a National Recreation Trail. It meanders along the lakeshore and through hillside igneous glades and descends into a deep ravine below the dam where Crane Pond Creek cascades through spectacular rhyolite shut-ins. East of the lake the trail connects to the Ozark Trail proper and continues to Marble Creek campground. All told, we would be hiking a 9-mile stretch.

I knew we were in a special place almost from the beginning when I noticed a small flowering plant growing next to the trail under the mixed pine/oak canopy. I’m not a very good botanist, but I instantly recognized the plant as dwarf spiderwort (Tradescantia longipes), an Ozark endemic known from only a handful of counties in Missouri and Arkansas. I knew this only because I had just the night before read about this wonderful plant on Ozark Highlands of Missouri, a superb natural history blog focused on my beloved Ozarks. Reading about this lovely, diminutive member of the genus, I wondered if I might encounter it on my own hike the next day. As we searched off the trail and near the lakeshore we encountered dozens of the plants, each with one or two exquisite blue flowers. Our excitement at seeing a true Ozark endemic increased with each plant we encountered, giving us confidence that its future, at least in this area, appears secure. Of the numerous photographs I took, I share two that show its short, squat habit and filament-covered stamens. Eventually we decided we needed to move on – we had spent 20 minutes and only hiked 100 ft!

Looping around the south side of the lake, the trail traversed mesic to dry-mesic upland forest and afforded spectacular views of the lake and rugged north shore. The spring ephemerals had already come and gone, replaced by such classic woodland denizens as birdfoot violet (Viola pedata, pictured), fire pink (Silene virginica), cream wild indigo (Baptisia leucophaea), four-leaved milkweed (Asclepias quadrifolia), Pursh’s phacelia (Phacelia purshii), and shooting star (Dodecatheon meadia). Insect life was abundant, however, the only species seen in one of my chosen specialties, metallic wood boring beetles (family Buprestidae), were early spring species of Acmaeodera – pictured here is A. ornata on a dewberry (Rubus sp.) flower. This pretty little beetle occurs throughout eastern North America in early spring on a variety of flowers, where adults feed on pollen and mate. Eggs are laid on dead branches of certain hardwood trees, through which the larvae tunnel as they develop. Dry, dead wood contains little nutritional value, and the larvae cannot digest the cellulose. As a result, they eat considerable volumes of wood, extracting whatever nutrients they can for growth and ejecting the bulk as sawdust, which they pack tightly in their tunnels behind them. A year or more might be required before they have grown sufficiently to transform into the adult and emerge from the wood. A smaller relative, Acmaeodera tubulus, was also seen on flowers of native dwarf dandelion (Krigia biflora).

We stopped for lunch on a little point extending out towards the lake. The forest overstory was dominated by an open mixture of white oak (Quercus alba) and shortleaf pine (Pinus echinata). Thickets of highbush huckleberry (Vaccinium stramineum) and carpets of reindeer moss in the open areas belied the acidic nature of the igneous substrate. Stands of bastard toad flax (Comandra richardsiana) in full bloom were found at the tip’s dry, rocky tip. These interesting plants feed parasitically on neighboring plants, attaching to the roots of their hosts by means of their long, thin rhizomes. Resuming our hike, we descended down into a shaded, moist draw feeding the lake and saw a huge royal fern (Osmunda regalis var. spectabilis) bush. I had never seen this aptly named fern before, but it was immediately recognizeable by its large size (~5 ft in height) and presence of distinctive, fertile leaflets on some of its upper branches – a very striking and handsome fern, indeed. Nearby was a smaller, but no less attractive species of fern that I take to be marginal sheild fern (Dryopteris marginalis) – another species I have not seen before (or at least made the effort to notice).

Soon, we reached the dam and for the first time saw the spectacular rhyolite shut-ins. While perhaps not quite as impressive as the nearby and much more famous Johnson’s Shut-Ins, Rich and I nonetheless watched entranced as the water roared over the smooth igneous rock exposure, forming elegant cascades, rushing through narrow chutes, and swirling into small pools. Steep canyon walls rose sharply on each side of the shut-ins, as if standing guard. Clambering amidst the pines and cedars that cloaked them, we found this maidenhair spleenwort (Asplenium trichomanes) nestled within a crack on a vertical rock face under continuous deep shade. Reaching the top of the bluffs, we were greated by one of my favorite of all Ozark habitats – the igneous glade. Glades are natural island communities surrounded by a sea of forest. Their shallow, dry, rocky soil conditions support plants and animals more adapted to prairie or desert habitats. Specific communities are influenced by the type of rock below – igneous and sandstone substrates support lichens, mosses, and other acid soil-loving plants, while limestone and dolomite substrates support a more calcareous flora. The photo here shows the massive boulder outcroppings typical of igneous glades and their weather-resistant bedrock. We hoped to see a collared lizard (Crotaphytus collaris), perhaps Missouri’s finest saurian reptile, but today was not the day. We did, however, see adults of the beautiful and aptly named splendid tiger beetle (Cicindela splendida) sunning themselves on the bare rock surfaces – flashing brilliant green and clay-red. The adults we saw had spent the winter deep inside tunnels dug into the rocky soil the previous fall and were now looking for mates. Male tiger beetles grab females by the neck, their jagged, toothy jaws fitting precisely in grooves on the female neck designed specifically for such. As I looked upon this prairie island within the forest, I thought about how the St. Francois Mountains were once themselves islands. I realized the landscape we were exploring today was itself a fossil – with rhyolitic ‘islands’ amidst a ‘sea’ of cherty dolomite laid down a half billion years ago in the warm, tropical, Cambrian waters that surrounded the St. Francois Islands, by then already a billion years old themselves. Yes, the Earth itself seems to have begun here.

Leaving the glade and once again entering the acid pine forest, we came upon one of the most striking floral displays that either of us have ever witnessed – wild azalea (Rhododendron prinophyllum) in the midst of full bloom! I have known about several colonies of this plant for many years now but had only seen them at the very end of the bloom period, with just a few, pitiful, limply hanging flowers still attached. Today, the plants were absolutely dazzling. The blossoms were not only visually attractive, a deep pink color, but also unexpectedly fragrant. We stood amongst several specimen plants as tall as ourselves, taking picture after picture amidst the clovelike aroma wafting around us.

We checked our watches – we were now 3 hours into our hike and had traversed just 2 miles. Clearly, this was not a sustainable pace, so we put our heads down and focused on covering ground. Once leaving the vicinity of Crane Lake, the trail became rather difficult to follow – it obviously receives little use, and in one stretch some logging activities had obliterated the trail completely. Were it not for the sporadic pieces of orange flagging tape tied just within sight of the previous, we would not have know where to go. At one point, we got completely off-track and had to backtrack a full half mile before we found the proper trail. The day put our contour map reading skills to their greatest test yet. It was difficult and strenuous terrain, with steep up and down grades and few long ridgetop stretches until (thankfully) the final 2 miles, which terminated in a long descent (more thankfully) to Marble Creek Campground. Despite the difficulties in following the trail and our not bringing enough water, I would have to rank this section a close second to the Taum Sauk stretch for its ruggedness, spectacular vistas, and unique plant communities. Yes, the St. Francois Mountains are truly the heart of the Ozarks.