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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About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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21 Responses to Friday Flower – Dwarf Spiderwort

  1. Mary says:

    Fascinating information about the Ozark Highlands – I never knew there was so much endemism there. And the sweet flower – how lovely. Those intriguing hairs remind me of images I’ve seen of otherwise innocuous flowers under UV light. Here’s a link to an evening primrose under UV that has those fine lines radiating out from the center: http://tinyurl.com/5ew8rw. Probably coincidence, but I find it interesting.

    • You could be on to something – the pattern on the primrose flower is suspiciously similar to the pattern of the filaments. I sure would like to see the spiderwort flower under UV light.

      • Tim Eisele says:

        With the advent of ultraviolet LEDs, you can easily get cheap UV pocket flashlights these days. I bought one just like the ones that the airport security people use from American Science and Surplus last year for just $15, and it works great. They still have them, just search on “uv flashlight”.

        I kind of envy you your biological diversity and endemic species. Northern Michigan is almost the opposite extreme from the Ozarks – what with having been scraped clean by the glaciers up until less than 10,000 years ago, we have practically no ecological history, and almost nothing is endemic here.

        For that matter, the bedrock in the western Upper Peninsula is all precambrian, so we don’t have any macroscopic fossils either. Its as if almost one billion years of earth history never even happened here.

        • Hi Tim – I’m not sure it’s as easy as that, since the human eye can’t detect UV reflection. Anything we would be able to see would merely be whatever waves in the visible spectrum that are being reflected. Digital photography is making it easier to obtain UV renditions, but it is not cheap or for the faint of heart – see this great “how to” article by pro photographer Bjørn Rørslett.

          The biodiversity of the Ozark Highlands is fascinating, but don’t sell upper Michigan short – what you lack in endemics, you more than make up for in scale, remoteness, and unparalleled beauty. Black spruce bogs, aspen forests ablaze in yellow… it’s a stunning landscape. I once did a collecting trip starting at Drummond Island off the eastern tip and worked my way across the Upper Peninsula to Marquette before dropping south. For the entire 9 days in early July I had sunny skies and temps in the upper 70s to lower 80s. It was spectacular!

          • Tim Eisele says:

            You’re right on the UV, I realized a few hours after leaving my earlier comment that I’d committed the classic blunder of confusing fluorescence under UV with UV reflectance. Whoops. Although, I suppose it’s possible that there may be some flowers that fluoresce under UV light, in which case the flashlight actually would show something.

            And I agree that it is beautiful up here (it’s one of the reasons I stay, after all). I just miss fossil hunting. And am a little sad that, for example, the book “Michigan Turtles and Lizards” would be more accurately titled “Michigan turtles and lizard”, because there’s only one native lizard species in the state.

      • Mary says:

        I’ve been thinking about this coincidence a little more. Could it be that the radiating lines themselves encourage the insect to zero in on the sepals and that the added inducement of nectar is not necessary? Why else are the radiating lines so common (although not universal) under UV light?

        It seems that honeybees have a spectral sensitivity to yellow, blue, and UV, with the sharpest sensitivity in UV (http://tinyurl.com/2cmbkv2). But what if blue itself is sharp enough that radiating lines will attract? In that case, one would expect no difference in Tradescantia longipes when seen under UV or when seen under visible light.

        The main difference in the lines created by the hairs in Tradescantia longipes and the lines seen in other flowers under UV is that the hairs are three dimensional while (I assume) the UV lines are not. The 3-D aspect of the hairs make Faden’s thoughts appealing.

        • I agree – the radiating lines are a common UV phenomenon, while the 3-dimensional hairs are unique. It seems too energetically expensive to serve only a “landing guide” purpose, which is why I think there must be some other functional purpose and that it has something to do with allowing the plant to achieve pollination without providing a nectar reward.

  2. Snail says:

    What an exquisite little flower.

    That’s a good level of endemism! I guess with all that calcium around, the area also has a lot of snails. (Not that I’m focussed or anything,, you understand!)

    • Thanks, Snail. As I understand it, there are over 100 species of lands snails in Missouri. Ron Oesch is our resident malacologist and is set to publish a book on Missouri’s land snails soon.

  3. jason says:

    What a beautiful flower. As always, fantastic photos, Ted.

    The endemism of the area is impressive. I’ve recently taken a serious look at the matter here in Texas and have grown increasingly interested in the subject overall.

    It’s especially intriguing about the flower having no nectar yet being capable of attracting pollinators. The theory about the hairs is interesting to say the least. It’s another example of why I’m amazed at how much we still have to learn, even when it comes to species that seem so readily available and easily studied.

    • Thanks for your always kind praise (although I admit to having not gotten the flash quite right on these and having to do a little more than the usual levels adjustments).

      Texas certainly has its share of endemics – between the Edwards Plateau, Trans-Pecos, and Lower Rio Grande Valley (perhaps only false endemics due to lack of knowledge from across the border), there are plenty of plants and animals whose distribution is simply “TX”. I love your great state!

  4. That’s really a neat little plant. If anything could tempt me to relocate away from the Blue Grass Region of Southern Ohio, it would be Ozark Barrens.

  5. Hmmm, interesting puzzle about the lack of nectar, yet still attractive to insects. The flower looks like it ought to have nectar…maybe its as simple as that.

    Those hairs are fascinating – I love that you can actually see the cells in your second photo.

    BTW, Ted, I’ve gone as far as putting a macro lens on my “wish list” at B&H. I think I’m gonna have to take the plunge sooner or later.🙂

    • Hi Amber. I’m still not sold on simple visual trickery – the 3-dimensionality of the hairs must either at least resemble something the insect is very interested in or serve some other functional role. But what do I know? When it comes to botany I’m just a dabbler.

      There’s no turning back now – you have to get the lens, and when you do you’ll wonder what took you so long!

  6. Dale says:

    With respect to patterns visible in UV — I had a student confuse UV visibility and UV fluorescence with respect ot butterfly wings. The dorsal wing surface of males of one of the two common Colias species has a UV pattern with the other one does not. My student got out a collection and a UV lamp to see if he could tell the difference. I watched skeptically, secure in my superior knowledge that he wasn’t going to see anything. My jaw dropped when he showed me the males of one species looked clearly different under UV than the male of the other species. (I can’t remember which was which – philodice or eurytheme, but the difference was remarkable and I was suitably chagrined.

  7. Mike B. says:

    I just planted some of this (or at least a variety of it) in my yard a couple of weeks ago. Now I’m going to have to take a sample inside and throw it into my sons’ microscope!

    Thanks.

  8. Pingback: Friday Flower – Cleft Phlox « Beetles In The Bush

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