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A ROCKHOUSE MICROHABITAT THE WEST CROSS IN OE NORTH CENTRAL TEXAS TIMBERS George M.DiggsJr. Robert O'Kennon J. "Rockhouses" or rockhouse clill formations are deep recesses in bedrock cliffs that can maintain microhabitats that are highly buffered from the extremes in temperature and moisture typical of the surrounding macroenvironment (Farrar As discussed by Walck in comparison with the out- 1998). et (1996), al. more side macroenvironment, rockhouse habitats tend to be shaded, have higher summer, and temperatures during the winter, lower temperatures during the have lower evaporation and higher humidities. Not only there rates of relative is some evaporation, but water often enters via groundwater seepage, in cases less providing a relatively stable supply of moisture. In addition, condensation on humidity The rockhouse can the rock walls further increases locally. result a is provide microclimatic conditions very different (more moderated) from those typically found in a given geographic area. There are numerous such rockhouse haoitats in various areas of the eastern United States, particularly in sandstone strata. Several recent papers (Walck and Farrar 1998) have discussed these rockhouses the interesting 1996; et al. now known Walck plant taxa to occur in them. According to et al. (1996), 11 plant taxa are endemic or nearly endemic to sandstone rockhouses in the east- number ern Particularly interesting the occurrence in rockhouses of a of U.S. is bryophytes and ferns with tropical affinities (Farrar 1998). common While such rockhouse environments relatively in the eastern U.S., seem unlikely in the West Cross Timbers of North Central Texas-particularly since hard surface rocks are unusual in most of the region. Such rocl<s, however, known can be found in the area as the Palo Pinto Country in the northwestern portion of the West Cross Timbers. This rather rugged region underlain by is the oldest rocks exposed in North Central Texas, deposited during the Pennsyl- made vanian Period. These rocks vary, but are "largely up of impure shales soft, alternating with harder, coarse, brown sandstone and conglomerates" (Hill 1901). In one area of western Parker County where Pennsylvanian sandstones/ conglomerates are exposed, deep recesses have formed that are worthy of the term rockhouse. Striking rock walls approximately 40 meters) form feet (12 tall narrow passageways and has been known number recesses. for a of years that It one unusual plant distributional record associated with environment. this is Cary ovata (Mill.) K. Koch, shag-bark hickory (Juglandaceae), disjunct to this is main area by about 100 miles (275 kilometers) from region of occurrence in its East Texas Lipscomb 2321 1977-BRlT). The also the westernmost (e.g., site is & Aspknium locality in Texas for platyneuron (L) Britton, Sterns, Poggenb., ebony spleenwort (Aspleniaceae) (Turner 2003). et al. The moderated microclimate of this sheltered rockhouse microhabitat stands in rather sharp contrast to the macroclimate of the exposed upland West Timbers macrohabitat/community While Cross yearly average precipitation & in the area is approximately 29 inches (74 cm) (Griffiths Orton 1968; Hatch et al. 1990), rainfall is unevenly distributed with summers typically being ex- tremely hot and dry As a result, the upland vegetation has a distinctly dry area aspect-a savannah/ woodland with stunted Quercus siellata (post oak) and Quercus mari landica (blackjack oak), an understory of grasses (Diggs et 1999), al. and even such xerophytic, mainly western species as Berheris trijoliolata Moric. (agarito), Echinocereus reichenhachii (Terscheck ex Walp.) Haage (lace cac- F. Juniperus asheij. Buchholz (mountain-cedar), Mimosa Gray tus), horealis A. (catclaw), Opuntia leptocaulis DC. (pencil cholla), Zanthoxylum hirsutum & Buckley and Ziziphus (prickly-ash), obtusifolia (Hook. ex. Torr. A. Gray.) A. Gray (lotebush). Several years ago, another disjunction was discovered by one of us A (O'Kennon). large population of Arisaema triphyllum Schott, jack-in-the- (L.) was pulpit (Araceae), found in the mesic microhabitat between rock walls (Figs. and same 2) in the extensive rockhouse as Carya ovata (voucher: O'Kennon 1 J6024— we BRIT). Interestingly, even though estimate the population approxi- at number mately 2,000 above ground stems (the of genetically distinct individuals is unknown), it had not been reported previously in the literature, possibly due to confusion with the related widespread species, Arisaema dracontium The was (L.) Schott, (green-dragon). locality information provided to Turner et The num- (2003) for inclusion in the Atlas the Vascular Plants ojTexas. large al. of bers of individual stems present and their occurrence through a rather exten- human sive area of the rockhouse argues against any type of recent interven- 100 during the first week of April), even fewer produce fruits (during one sea- son only three individuals were observed with mature and most repro- fruits), duction probably by vegetation means. At the digging indicated that rhi- is site, zomes/underground stolons could be traced between different stems signifying expansion vegetative of the population. Additionally, several transplanted produced plants offsets (traceable to the original plant) the following spring cm 40-50 approximately from the parent plants. thus seems clear that the It reproducing and number plants are vegetatively, that the of genetically different individuals probably can be determined only by molecular analyses. The apparent lack of extensive sexual reproduction interesting in light of Krai's is (1956) observation that other species in East Texas were also apparently relict reproducing predominantly means. The between via vegetative disjunction the known western Parker County and the nearest East Texas location (Hend- site erson County) approximately 140 miles (225 kilometers). The occurrence of is this species in the West Cross Timbers quite unexpected given preference is its low or moist woods. However, the special microclimate (particularly reduced lor and cvapotranspiration persistent substrate moisture) apparently has allowed the long term survival of this mesic species in an otherwise rather inhospitable triphyllum controversial. Detailed study of is led Huttleston (1949, 1981, 1984) to conclude was that the variation seen in the species best represented by recognizing a single species with four subspecies; he indicated that of the four sub- "...plants and species are very distinctive readily identified, at least in living condition. many Since of the key characteristics...are obscured or lost during drying, it is not always possible to identify herbarium specimens to subspecies." At the other "much taxonomic extreme, because overlap occurs in expression of the charac- supposedly numerous teristics defining infraspecific taxa," because interme- diate forms exist, and because the ranges of the subspecies overlap, Thompson C2000) recently recognized a single variable species without infraspecific taxa. depending upon Thus, one's treatment of the variation present, the disjunct Parker County population would be either Arisaema triphyllum (no subspecies recognized) or A. triphyllum subsp. triphyllum. In a forthcoming flora of we East Texas, are treating the taxon as A. triph^Hum subsp. triphyllum. As discussed by Krai MacRoberts and MacRoberts and (1966), (1997), oth- numerous which ers, Texas has plant occurrences represent relicts of past cli- & matic conditions. Further, from the study of Texas bogs Potzger Tharp (e.g., & & HoUoway Bryant Holloway Bryant Bryant and from 1954; 1977; 1984; 1985) knowledge of modern day plant distributions Turner 2003), clear (e.g.. et al. it is FiG.Z.CIoseup o^Arisaema triphyllum (photo by R. that Texas vegetation was profoundly influenced by the climatic change associated with glaciation, even though actual glaciers were hundreds of miles to The County Arisaema the north of Texas. Parker occurrence of triphyllum thus & probably represents an Age holdover" (MacRoberts MacRoberts 1997) "Ice when from a colder and wetter period of the Pleistocene vegetational areas were and known, shifted considerably to the south west. for example, that at It is mean was C 15,000 years before present, the annual air temperature of Texas 5° less than at present, conditions were moister, and there was a more widespread & forest mosaic over most of Texas (Bryant 1977; Stable Cleaveland 1995). Other many modern day reflections of such past conditions can be seen in the species and genera typical of East Texas showing up in isolated disjunct pockets on the Hamamdis many Edwards Plateau virginiana L, witch-hazel) as well as (e.g. and communities (Palmer Diggs other interesting disjunct species 1920; 2002). window While rare in Texas, rockhouses do provide an interesting into bio- geographic history. As noted by Farrar (1998), the disjunct occurrences of plant species in rockhouses "document, as clearly as do a record of changing fossils, When phenomenon climate and vegetation." this taken together with the is study of bogs, and an understanding of other current day plant distributions, the impact of glacial history on the vegetation of Texas becomes increasingly understandable. Thanks James Peck and Donald Far to making helpful suggestions. Texas: An overview of the pollen evidence. V.M. Bryant, and R.G. Holloway, eds. In: Jr. Pollen records of late-Quaternary North American sediments. Pp. 39-70. American Assoc, of Stratigraphic Palynologists Foundation, Dallas, TX. )k G.M., Jr. 2002. East Texas as a unique habitat. In: Native Plant Society of Texas. Special ,s, ,( Symposium 53-66. 2002 Proceedings, Houston. habitats. Pp. G.M., omb, and O'Kennon. 999. Shinners & Mahler's illustrated flora of )K ,( ,s, Jr., B.L. Lii'sc R.J. 1 North Central Texas. Sida, Bot. Misc. 6. 1 ARRAR, D.R. 998. The tropical flora of rockhouse cliff formations in the eastern United 1 25:91-1 States. Bull.Torrey Bot. Soc. 08. 1 J.F.and R.Orton. 1968. Agroclimatic atlas of Texas-Part Precipitation probabili- jRirriTHs, I. ties.Texas Agric. Exp. Sta. Misc. Publ. No. 888. Iakh, K.N.Ganuhi, AND L.E.Brown. 1990. Checklist of the vascular plants of Texas. Texas S.L., Agric. Exp. Misc. Publ. 1655:1 -158. Sta. 901 .Geography and geology of the Black and Grand prairie5,Texas.21 Annual R.T. st Ill 1 , I Government Report of the U. Geological Survey, Part Vll-Texas. U. Printing Office, S. S. Washington, D.C. JditowAY, R.G. and V.M. Bryant. 1984. P/ceag/auca pollen from late-glacial deposits in cen- Palynology 8:21-32. Texas. tral -lurrLESTON, D.C. 1949. The three subspecies of Arisaema triphyllum. Bull.Torrey Bot. Club 76:407-413. HufTLESTON, D.C, 1981. The four subspecies of Ansaemo triphyllum. Bull.Torrey Bot. Club Aroideana 7:14-18. Pulpit." 1966. Observations on the flora of the southeastern United States with special sRAL, R. reference to northern Louisiana. Sida 2:395-408. and beech-hardwood ylAcRoBERTS, B.R. M.H. MacRoberts. 1997. Ftoristics of forests in East Texas. Phytologia 82:20-29. 1920.The canyon of the Edwards Plateau ofTexas.J. Arnold Arbor. :233- 'aimer, flora E.J. 1 PoTZGER,J.E.andB.C.THARP,1943.Pollen record c Science 98:584-585. and Stahee, D.W. M.K. Cleaveland. 1995, Texas p N NORTH CENTRAL TEXAS climate of Texas: Predictability and implications the future. Chapter Pp. 7, A&M GeoBooks, Texas Unlv.Xollege Station. Thompson, 2000.Araceae. Flora of North Ameri' S.A. In: New Amer. 28-142. Oxford York 22:1 Univ. Press, ar Turner, H.Nichols, G.Denny, and O.Doron. 2003. All B.L., gymnosperms, monocots. Dicots, Vol. Ferns, S 2: 1 : and Sandston Walck, J.L, J.M. Baskin, C.C. Baskin. 996. 1 States with particular reference to the ecology e taxa.Bot.Rev.62:311-362.