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Yucca, Yucca

Sunday, June 13, 2010 3:39 PM | Anonymous
Panorama of twist-leaf yucca at Doeskin Ranch in June.

     How impressive is the flowering of twist-leaf yucca right now?!  If you haven’t done so recently, drive FM 1174 up to Doeskin Ranch and you’ll see the most amazing display of blooms of this Hill Country endemic yucca in decades.

Blooms of twist-leaf yucca.     In a typical year only a small portion of the yucca plants successfully flower and set seed.  Yucca flower stalks, it seems, are “deer candy”.  Whitetails normally wander the hills and dales munching on the stalks just as they start to grow in April and May.  The sight of a yucca stalk bitten off about one to two feet above the leaves is the more typical aspect we expect at this time of year.  Usually, the only yuccas that successfully bloom are those where deer can’t get to them: growing in the middle of a big pricklypear clump, on a cliffside, in a fenced deer-proof exclosure, or along a busy roadside where a deer doesn’t feel comfortable foraging.

     Why is the bloom of the yucca so spectacular this year?  I can only speculate.  It has been an abundant year for all wildflowers due to the wet winter and early spring.  That’s certainly part of the reason.  But I think we can take the abundance of yucca stalks right now as a measure of a lowered deer herd due to the drought conditions of 2008-09, at least locally.  As well, any number of other smaller critters (like the yucca moth, yucca skipper, weevils, etc.) which feed on various parts of yucca plants and might take a chunk out of it's reproduction may have suffered declines along with the deer herd.  The yuccas have been released to grow and spread their pedicels*.

     We have actually identified four species of yucca in the Refuge area.  Perhaps 99% of the yuccas you’ll see across the Refuge are twist-leaf (Yucca rupicola), a species endemic to the Edwards Plateau.  Most of the time, but not always, you can recognize this species by the slight twist in each leaf which contorts on some plants to nearly a full twirl.

Buckley yucca. Credit: Joseph A. Marcus; Ladybird Johnson Wildflower Center Digital Library.

     Co-occurring on several of the more northerly tracts in the Burnet County portion of the Refuge is Buckley yucca (Y. constricta).  This is another Texas endemic.  It can be recognized by its narrow, straight leaves which have curling threads along the margins.  These yuccas have a tall flower stalk like twist-leaf.  I recently noticed several Buckley yuccas along the lower portion of the Rimrock Trail at Doeskin Ranch.  Follow the jeep trail from the trailhead down across the creek and watch for this species on the right as the trail gently ascends the open grassland on the far (east) side.

Arkansas yucca. Credit: Sally & Andy Wasowski; Ladybird Johnson Wildflower Center Digital Library.     A third small yucca, that is, a yucca without a tree-like trunk, is Arkansas yucca (Y. arkansana).  I think it was John Kelly who pointed out a small population of this species to me at one of our favorite botany spots along Cow Creek Road.  As you drive up Cow Creek Road from RM 1431, the first 0.5 mile passes over some sandier substrates derived from non-limestone terrain--more on that in a later blog.  It is characterized by several species of plants which occur on these sandy lands and almost nowhere else in the Refuge area.  The second bend of the road has acquired our local nickname of “Greeneyes Bend” because of the conspicuous population of the namesake plant (Berlandiera betonicifolia) which blooms for much of the spring and summer there.  Tucked in amongst the greeneyes are several low yuccas which key out to Arkansas yucca.  This species can be recognized by a combination of leaves with threads on the edges and a short flower stalk with flowers starting just barely above the leaves and with a fairly simple flower arrangement with few/no side branchlets.

     The last of the four yuccas and the least numerous is Torrey yucca Flowers of Spanish dagger. Credit: Rick Hammer from his or Spanish dagger (Y. torreyi), a species that is much more common in cultivation and in the sandy soils of the Llano uplift and further west.  [I think this plant is erroneously identified as Trecul yucca on a recent edition of our Refuge plant list.]  This is an arborescent yucca, old examples of which can have a leafy trunk up to 8 or 10 feet tall or more.  The leaves are huge and straight and the plants have abundant flowers in summer in a huge bundle.  While looking for nice pictures of Spanish dagger to include with this blog, I came across Rick Hammer’s wonderful botanical blog on the "Flora of the Texas Rolling Plains".  Rick is a Professor at Hardin-Simmons University in Abilene, Texas.  Check it out.

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Below The Line:

    * How's your botanical terminology?  A "pedicel" is the stalk of an individual flower.  A "peduncle" is the flowering stem for a cluster of flowers (like the yucca stalk) or the stalk of a single flower when there is only one (like a poppy, for instance).  A "petiole" is the stalk of a simple leaf (as you find on an oak or elm tree) or the central stalk of a compound leaf (like a pecan, walnut, or soapberry) and a "petiolule" is the stalk of an individual leaflet on a compound leaf.  Now you know; you are now smarter than my spell-checker.


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