Chilopsis Research Articles

Using the Hydraulic Properties of Zeolite to Grow Desert Willow—A Case Study to Rehabilitate Riparian Areas of Semi-Arid Environments

Plants in riparian areas are well known for their beneficial functions such as providing biodiverse habitats, maintaining water quality, and stabilizing streambanks. However, riparian plants are declining in semi-arid environments due to long-term drought, a decline in groundwater table, and an increase in soil salinity. A new technique using clinoptilolite zeolite (CZ) as a wicking material with minimum artificial irrigation to grow desert willow [Chilopsis linearis (Cav.) Sweet] under field conditions is introduced; desert willow is native to riparian regions of the southwestern United States. For this study’s experiment, desert willow seedlings were planted in boreholes filled with clinoptilolite zeolite (CZ) as a substrate and in situ riparian sandy loam soil (RS) as a control. The boreholes extended to the groundwater table at two distinctive depths, shallow (avg. depth = 1.21 m) and deep (avg. depth = 2.14 m). The plants’ viability was then assessed by measuring their midday water potential (Ψmd) as an indicator of water stress. There was no significant difference in Ψmd (p > 0.05) between the plants grown in CZ and RS (mean Ψmd = −0.91 vs. −0.81 MPa) where the groundwater was shallow and a significant difference (mean Ψmd = −0.75 vs. −2.03 MPa) where the groundwater was deep. The proposed method is promising as an alternative method for growing desert willow or other plants for riparian rehabilitation with no artificial irrigation. However, its effectiveness depends on groundwater being accessible at the base of the boreholes used for planting.

Phenology and description of a new species of Hoplothrips (Thysanoptera: Phlaeothripidae) in Mojave Desert leaf litter

A description and diagnosis are given for Hoplothrips cooperi sp. nov. collected from leaf litter beneath Chilopsis linearis (Cavanilles) Sweet (Bignoniaceae) shrubs in the Mojave Desert in southern Nevada. All adult males and most adult females are apterous, with macropters produced only in females. I examined the phenology of the species at a single locality during 27 November 2018 to 19 June 2019. Three generations were evident during winter and spring from the densities of larval and pupal instars. The timing and abundances of these generations appeared dependent on rainfall, consistent with thrips feeding on fungi growing on moist, dead leaves and stems. Most apterous adults and all macropterous females were collected during late spring when thrips densities and leaf-litter temperatures were highest. Hoplothrips cooperi appears to be the first species in the genus to be collected from leaf litter in the western U.S. and Mexico.

Genome-wide transcriptomic analysis of a desert willow, Salix psammophila, reveals the function of hub genes SpMDP1 and SpWRKY33 in drought tolerance

BackgroundDrought is a major environmental constraint to plant growth, development and productivity. Compared with most willows that are generally susceptible to drought, the desert willow Salix psammophila has extraordinary adaptation to drought stress. However, its molecular basis of drought tolerance is still largely unknown.ResultsDuring polyethylene glycol 6000 (PEG 6000)-simulated drought stress, we found that the osmotic adjustment substances were accumulated and the antioxidant enzyme activities were enhanced in S. psammophila roots. A total of 8172 differentially expressed genes were identified in roots of S. psammophila through RNA-Sequencing. Based on K-means clustering, their expression patterns were classified into nine clusters, which were enriched in several stress-related processes including transcriptional regulation, response to various stresses, cell death, etc. Moreover, 672 transcription factors from 45 gene families were differentially expressed under drought stress. Furthermore, a weighted gene co-expression network was constructed, and eight genes were identified as hub genes. We demonstrated the function of two hub genes, magnesium-dependent phosphatase 1 (SpMDP1) and SpWRKY33, through overexpression in Arabidopsis thaliana. Overexpression of the two hub genes enhanced the drought tolerance in transgenic plants, suggesting that the identification of candidate drought tolerance genes in this study was highly efficient and credible.ConclusionsOur study analyzed the physiological and molecular responses to drought stress in S. psammophila, and these results contribute to dissect the mechanism of drought tolerance of S. psammophila and facilitate identification of critical genes involved in drought tolerance for willow breeding.

Determination of triacylglycerols and fatty acid composition ofChilopsis linearisseed oil by reverse-phase high-performance liquid chromatography

In the present work, the compositions of the 27 triacylglycerols (TAGs) as well as fatty acid composition of Chilopsis linearis seed oil were determined by reverse-phase high-performance liquid chromatography (RP-HPLC) with diode array and mass spectrometric detections. It was shown that the main conjugated acid in the seed oil is a catalpic acid, (9E,11E,13Z)-octadeca-9,11,13-trienoic acid, while two unusual fatty acids have the parameters satisfying the literature data for (10E,12E)-octadeca-10,12-dienoic and (9E,12E)-octadeca-9,12-dienoic acids. For the two conjugated acid substituents the isosbestic point (at 234 nm) was found and was used to calculate the ratios of TAGs with different chromophores in the oil, taking into account the peak areas on the oil chromatogram.

Analysis of the genetic diversity and population structure of Salix psammophila based on phenotypic traits and simple sequence repeat markers.

Salix psammophila (desert willow) is a shrub endemic to the Kubuqi Desert and the Mu Us Desert, China, that plays an important role in maintaining local ecosystems and can be used as a biomass feedstock for biofuels and bioenergy. However, the lack of information on phenotypic traits and molecular markers for this species limits the study of genetic diversity and population structure. In this study, nine phenotypic traits were analyzed to assess the morphological diversity and variation. The mean coefficient of variation of 17 populations ranged from 18.35% (branch angle (BA)) to 38.52% (leaf area (LA)). Unweighted pair-group method with arithmetic mean analysis of nine phenotypic traits of S. psammophila showed the same results, with the 17 populations clustering into five groups. We selected 491 genets of the 17 populations to analyze genetic diversity and population structure based on simple sequence repeat (SSR) markers. Analysis of molecular variance (AMOVA) revealed that most of the genetic variance (95%) was within populations, whereas only a small portion (5%) was among populations. Moreover, using the animal model with SSR-based relatedness estimated of S. psammophila, we found relatively moderate heritability values for phenotypic traits, suggesting that most of trait variation were caused by environmental or developmental variation. Principal coordinate and phylogenetic analyses based on SSR data revealed that populations P1, P2, P9, P16, and P17 were separated from the others. The results showed that the marginal populations located in the northeastern and southwestern had lower genetic diversity, which may be related to the direction of wind. These results provide a theoretical basis for germplasm management and genetic improvement of desert willow.

The Older, the More

The Older, the More Amy Uyematsu (bio) Keywords poetry, Amy Uyematsu ishigokoro: the 'heart' or 'mind' of the rock "Years, months, days, and hours are nothing but the mind." —Dogen, 13th-century Japan lately I feel I belongto a mind so big— many calling it sacred others, love or breath or love and breath and their unending need to go on… …. the more I spend time with treesor stones the more I'm certain of tree mind, stone mind complex as my own… …. take a tree, for instancelike the desert willow I just planted surely it knows the violent upheaval from one pot to the next [End Page 677] surely it carries the centuries its ancestors flourished in distant soil look, three new buds about to explode part pink, part purple so surely attentive… …. some days I am struckwith the half-open fragments my world moored in paradox and yetso many cues whether a small perfect pebble catching my eye or that small truthI stumble on, promise not to forget our connections… …. is this one encompassing mindor is our starlit galaxy to be found in the incomparable particulars [End Page 678] my brief seven decades dizzying while still deliberate and unexpected pine trees black stones white rice new poems… …. the sky makes it obviousjust follow the clouds infinite mind shifting between turbulence, calm no wonder I watch so closely now and feel so at home [End Page 679] Amy Uyematsu amy uyematsu is a sansei (third-generation Japanese American) poet and teacher from Los Angeles. She has five published collections: 30 Miles from J-Town; Nights of Fire, Nights of Rain; Stone Bow Prayer; The Yellow Door; and Basic Vocabulary. She was a coeditor of the widely used UCLA anthology Roots: An Asian American Reader. A former public high school math instructor, she currently leads a writing workshop at the Far East Lounge in LA's Little Tokyo. Copyright © 2018 The Massachusetts Review, Inc.

Livestock effect on floristic composition and vegetation structure of two desert scrublands in northwest Coahuila, Mexico

Abstract Microphyllous and rosetophyllous desert scrub plant communities dominate large parts of the state of Coahuila, Mexico, yet differences in how livestock grazing impacts these two plant communities are not well documented. In order to address this knowledge gap, we assessed livestock impact on plant species composition and vegetation structure in microphyllous and rosetophyllous desert scrublands in this northwestern Mexican state. We collected plant density, frequency, and cover data from sites with and without livestock grazing pressure that were otherwise similar in plant composition. We quantified intersite differences using the importance value index (IVI) and the Bray-Curtis similarity index. The species with the highest IVI for microphyllous scrubland were lechuguilla (Agave lechuguilla), honey mesquite (Prosopis glandulosa), and creosote bush (Larrea tridentata); however, in sites with presence of domestic herbivores, desert willow (Chilopsis linearis) and spiny hackberry (Celtis pallida) a...

Hitchhikers at the dinner table: a revisionary study of a group of ant parasitoids (Hymenoptera: Eucharitidae) specializing in the use of extrafloral nectaries for host access

Abstract.Extrafloral nectaries (EFNs) are nectar‐secreting glands found on plants independent of their flowers. EFNs are diverse in form, present on a wide variety of plants, and their secretions are known to recruit ants. However, much less information has been published on insects with known EFN associations other than ants. Two distinct species groups of Orasema Cameron (Hymenoptera: Eucharitidae) deposit their eggs close to the EFNs of their plant hosts. The simulatrix group comprises six species found in deserts and xeric shrublands of the southwestern United States and Mexico. This species group is revised, retaining O. aureoviridis, O. beameri and O. simulatrix as valid species, and describing O. cancellata sp.n., O. difrancoae sp.n. and O. zahni sp.n. The wayqecha group is from Peru and Colombia and includes the newly described O. wayqecha sp.n. and O. quadrimaculata sp.n. Members of the simulatrix group oviposit near EFNs of Chilopsis linearis Cav. (Bignoniaceae), Prosopis glandulosa Torr. (Fabaceae), Prosopis velutina Wooton (Fabaceae) and Populus angustifolia James (Salicaceae), whereas Orasema wayqecha oviposit on leaves of two species in the family Primulaceae. Monophyly of the two species groups is proposed based on a molecular analysis of ribosomal (28S and 18S) and mitochondrial (cytochrome c oxidase subunit I) DNA, morphological features of the adults and planidia larvae, and their shared behavioural association with EFNs. Adults of both species groups have an expanded postgena that encloses the mouthparts, but are otherwise morphologically divergent. The planidia of both groups also share several features, including long cerci that may facilitate their movements within EFNs. Oviposition near EFNs is proposed as a means of increasing encounter rates of the first‐instar larvae with their myrmicine ant host; however, it remains unclear whether the planidia are transported directly by the foraging workers of their host Pheidole (Formicidae: Myrmicinae) or indirectly with the help of an intermediate host.This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:EA112E3D-52BE-45D1-B03B-8764E8C94BE0.

De novo transcriptome assembly, development of EST-SSR markers and population genetic analyses for the desert biomass willow, Salix psammophila.

Salix psammophila, a sandy shrub known as desert willow, is regarded as a potential biomass feedstock and plays an important role in maintaining local ecosystems. However, a lack of genomic data and efficient molecular markers limit the study of its population evolution and genetic breeding. In this study, chromosome counts, flow cytometry and SSR analyses indicated that S. psammophila is tetraploid. A total of 6,346 EST-SSRs were detected based on 71,458 de novo assembled unigenes from transcriptome data. Twenty-seven EST-SSR markers were developed to evaluate the genetic diversity and population structure of S. psammophila from eight natural populations in Northern China. High levels of genetic diversity (mean 10.63 alleles per locus; mean HE 0.689) were dectected in S. psammophila. The weak population structure and little genetic differentiation (pairwise FST = 0.006–0.016) were found among Population 1-Population 7 (Pop1-Pop7; Inner Mongolia and Shaanxi), but Pop8 (Ningxia) was clearly separated from Pop1-Pop7 and moderate differentiation (pairwise FST = 0.045–0.055) was detected between them, which may be influenced by local habitat conditions. Molecular variance analyses indicated that most of the genetic variation (94.27%) existed within populations. These results provide valuable genetic informations for natural resource conservation and breeding programme optimisation of S. psammophila.

Effects of wildfire on riparian trees in southeastern Arizona

We measured fire damage to 250 riparian trees in 2003–2004, and again in 2012–2013, in a southeastern Arizona grassland burned by wildfires in 2002, 2009, or both. Following a single fire, combined mortality or survival only by ground-level resprout was 64% for desert willow (Chilopsis linearis), 57% for Fremont cottonwood (Populus fremontii), 48% for Arizona walnut (Juglans major), 32% for velvet ash (Fraxinus velutina), and 25% for Wright's sycamore (Platanus wrightii). A second fire burned 120 of the trees that happened to have been less damaged by the first fire. Distinctions among species in overall fire damage persisted after the second fire but to a lesser degree. By the conclusion of our study, 26% of the 250 trees had died completely while another 32% survived only as relatively small resprouts. We conclude that the fires substantially reduced both the abundance and crown volume of mature riparian trees in the study area.

Chemical Composition of Desert Willow (Salix psammophila) Grown in the Kubuqi Desert, Inner Mongolia, China: Bark Extracts Associated with Environmental Adaptability

Bark of desert willow (Salix psammophila, Spsa) grown in Inner Mongolia was successively extracted with n-hexane, diethyl ether, acetone, methanol, and hot water to examine chemical components associated with its environmental adaptability to desert conditions. The yield of n-hexane extract (5.0% based on dry bark), mainly composed of wax, was higher than those of acetone and methanol extracts (3.7% and 4.2%, respectively), whereas the yields of n-hexane extract (1.4%) from willow bark grown in humid areas were much lower than those of acetone (17.4% and 19.9%) and methanol (12.5% and 14.0%) extracts. Unlike other willow bark samples, Spsa bark contained a certain amount of sugar alcohols. In particular, we identified arabinitol (0.21%), which has not previously been reported as a major component of extracts of willow bark. The high content of wax and sugar alcohol would be associated with the ability of Spsa to survive in desert conditions. Accumulation of wax on the outer bark surface would reduce water loss, while sugar alcohols might improve freezing tolerance.

Determination of elements in situ in green leaves by laser ablation ICP-MS using pressed reference materials for calibration

Laser ablation (LA) was used with double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) for direct elemental analysis of green leaves from seven species of desert plants. Pressed leaf standards (n = 7) were used as matrix matched standards for calibration and quality assurance. Nine elements (Mg, Ca, Mn, Cu, Sr, Cd, Ba, Hg and Pb) were determined in low mass resolution (m/Δm ≈ 400). Data was collected for three ablation line scans starting from near the stem to the tip of the leaf. The 213 nm laser ablation system was operated at the full energy setting (100%), with a repetition rate of 20 Hz, a spot size of 100 μm, and a scan rate of 50 μm min−1. Pressed cellulose was used for estimating detection limits, which were found to vary between 0.04 and 26 μg g−1 for Pb and Ca, respectively. Results suggest that the calibration approach is feasible for some elements (Mg, Ca, Mn, Cu, Sr, Cd, Ba) but problematic for others (Pb, Hg). Although somewhat element dependent, desert willow, autumn sage and brittle bush tended to have the highest concentrations of the elements monitored. Overall, LA-ICP-MS is a useful method for quantifying (in situ) the distribution of many elements in plant leaves.

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow)

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow) . A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As 2O 5, As V) at 0, 20, and 40 mg As V L −1. Results from the ICP-OES analysis showed that at 20 mg As V L −1, red flowered plants had 280 ± 11 and 98 ± 7 mg As kg −1 dry wt in roots and stems, respectively, while white flowered plants had 196 ± 30 and 103 ± 13 mg As kg −1 dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As V L −1, As was at 290 ± 77 and 151 ± 60 mg As kg −1 in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406 ± 36, 213 ± 12, and 177 ± 40 mg As kg −1 in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX) 3 species in both types of plants.

Emission of sunscreen salicylic esters from desert vegetation and their contribution to aerosol formation

Abstract. Biogenic volatile organic compounds (BVOC) produced by plants are known to have an important role in atmospheric chemistry. However, our knowledge of the range of BVOCs produced by different plant processes is still expanding, and there remain poorly understood categories of BVOCs. In this study, emissions of a novel class of BVOC emissions were investigated in a desert region. Our study considered 8 species of common desert plants: blackbrush (Coleogyne ramosissima), desert willow (Chilopsis linearis), mesquite (Prosopis glandulosa), mondel pine (Pinus eldarica), pinyon pine (Pinus monophylla), cottonwood (Populus deltoides), saguaro cactus (Carnegiea gigantea) and yucca (Yucca baccata). The measurements focused on BVOCs with relatively high molecular weight (>C15) and/or an oxygenated functional group. Significantly high emission rates of two salicylic esters were found for blackbrush, desert willow and mesquite with emission rates of 3.1, 1.0 and 4.8μgC dwg−1 h−1, respectively (dwg; dry weight of the leaves in gram). The salicylic esters were identified as 2-ethylhexenyl salicylate (2-EHS) and 3,3,5-trimethylcyclohexenyl salicylate (homosalate) and are known as effective ultraviolet (UV) absorbers. We propose that the plants derive a protective benefit against UV radiation from the salicylic esters and that the emission process is driven by the physical evaporation of the salicylic esters due to the high ambient temperatures. In addition, the salicylic esters are predicted to be an effective precursor of secondary organic aerosol (SOA) because they probably produce oxidation products that can condense onto the aerosol phase. We estimated the contribution of the sunscreen esters themselves and their oxidation products on the SOA formation for the Las Vegas area using a BVOC emission model. The contribution was estimated to reach 50% of the biogenic terpenoid emission in the landscapes dominated by desert willow and mesquite and 13% in the Las Vegas area. The contributions to biogenic SOA are likely to be higher due to the potentially high SOA yields of these compounds.

Effect of mercury and gold on growth, nutrient uptake, and anatomical changes in Chilopsis linearis

Plants of Chilopsis linearis were grown with 0, 50, 100, and 200 μM Hg [as Hg(CH 3COO) 2] and 0 and 50 μM Au (as KAuCl 4) in hydroponics. The results showed that seedling grown with 50 μM Au + 50 μM Hg and 50 μM Au + 100 μM Hg had roots 25 and 55% shorter than control roots, respectively. The element uptake determination using ICP/OES demonstrated that Hg at 50 and 100 μM (with and without Au) significantly increased ( p < 0.05) the S concentration in leaves. On the other hand, the concentration of Fe significantly increased in roots of plants treated with Au–Hg. In addition, the stems of plants treated with Hg at 100 μM, with and without Au, had 239 and 876 mg Hg/kg dry biomass (d wt), respectively. Also, at 50 μM Hg, with and without Au, stems accumulated 375 and 475 mg Hg/kg d wt. The Hg concentration in leaves (287 mg Hg/kg d wt) was higher ( p < 0.05) for the treatment containing 50 μM Au + 100 μM Hg. Without Au, the Hg concentration in leaves decreased to 75 mg Hg/kg d wt. Toxicity symptoms induced by Hg in cortex cells and the vascular system were lower in plants exposed to 50 μM Au + 50 μM Hg compared to plants exposed to 50 μM Hg only. Further, the SEM micrographs revealed deposition of Au–Hg particles inside the root. Although the concentrations of Hg used in this study showed different degree of toxicity, the plants displayed good agronomic value.

Potential of Chilopsis Linearis for Gold Phytomining: Using Xas to Determine Gold Reduction and Nanoparticle Formation Within Plant Tissues

This study reports on the capability of the desert plant Chilopsis linearis (Cav.) Sweet (desert willow) to uptake gold (Au) from gold-enriched media at different plant-growth stages. Plants were exposed to 20, 40, 80, 160, and 320 mg Au L−1 in agar-based growing media for 13, 18, 23, and 35 d. The Au content and oxidation state of Au in the plants were determined using an inductively coupled plasma/optical emission spectrometer (ICP/OES) and X-ray absorption spectroscopy (XAS), respectively. Gold concentrations ranging from 20 to 80 mg Au L−1 did not significantly affect Chilopsis linearis plant growth. The concentration of gold in the plants increased as the age of the plant increased. The Au concentrations in leaves for the 20, 40, 80, and 160 mg Au L−1 treatments were 32, 60, 62, and 179 mg Au kg−1 dry weight mass, respectively, demonstrating the gold uptake capability of desert willow. The XAS data indicated that desert willow produced gold nanoparticles within plant tissues. Plants exposed to 160 mg Au L−1 formed nanoparticles that averaged approximately 8, 35, and 18 Å in root, stem, and leaves, respectively. It was observed that the average size of the Au nanoparticles formed by the plants is related to the total Au concentration in tissues and their location in the plant

Improving gold phytoextraction in desert willow (Chilopsis linearis) using thiourea: a spectroscopic investigation

Environmental context. The conventional methods used for the extraction of gold from mine tailings and runoff are costly and often require harsh chemical treatment. Using plants to extract gold is more environmentally friendly and economically feasible. Plants are especially appealing because they can uptake low levels of gold and accumulate them in their tissues, whereas conventional methods are less effective at extracting gold at low levels. Thiourea has been proposed as an alternative gold chelator that could help in gold phytomining. It is less toxic than cyanide, which is the chemical commonly used to dissolve gold from mine ores. Abstract. Phytomining, the use of plants to recover noble metals, is developing as a feasible option to extract gold from mine tailings. In this study, thiourea (TU) was used to increase gold availability and to enhance gold accumulation by the desert plant Chilopsis linearis. Seedlings of C. linearis were grown in a hydroponic solution containing 25 μM Au and TU at 25, 50, 100, 200, and 400 μM. After two weeks of growth, the concentration of Au, micro- and macronutrients was determined using inductively coupled plasma–optical emission spectroscopy. In addition, X-ray absorption spectroscopy was used to determine the oxidation state and the coordination of the Au atom within the plant tissues. The effect of TU on plant growth was determined as well. The results of the present study demonstrated that TU at 25 μM was able to increase the Au uptake by C. linearis plants grown in hydroponics without any toxic effect. However, the translocation to stem and leaves was better at 100 and 200 μM of TU, respectively. The addition of TU to hydroponic solutions did not affect the uptake of Ca, Mg, P, and K. However, TU induced an increase in uptake of S, Fe, Cu, and Zn and a decrease in Mn uptake. When Au was chelated with TU, the plant transformed 64% of the Au–TU complex to Au(0) and the other 36% remained in the ionic form.

Reproductive Behavior of Induced Allotetraploid ×Chitalpa and In Vitro Embryo Culture of Polyploid Progeny

×Chitalpa tashkentensis Elias &amp; Wisura is a sterile intergeneric hybrid [Catalpa bignonioides Walt. × Chilopsis linearis (Cav.) Sweet]. To restore fertility in ×Chitalpa the following were evaluated: 1) oryzalin as a polyploidization agent, 2) fertility of induced polyploids, and 3) in vitro culture methods for embryo rescue of interploid crosses. Meristems of ×Chitalpa `Pink Dawn' were submerged in an aqueous solution of 150 μm oryzalin for 0, 6, 12, or 24 hours and ploidy analyzed via flow cytometry. As treatment duration increased, recovery of diploids decreased as mixoploids and shoot mortality increased. Two tetraploid shoots occurred in the 24-hour treatment. Four tetraploids and two cytochimeras were stabilized in total. Tetraploids flowered sparsely; however, cytochimeras flowered profusely and these were used to study fertility at the tetraploid level. Diploid ×Chitalpa `Pink Dawn' pollen was essentially nonviable, but cytochimera pollen stained and germinated equal to or greater than pollen of C. bignonioides and C. linearis `Bubba'. Cytochimera ×Chitalpa were selfed yielding tetraploid seedlings, crossed with C. bignonioides to yield triploids, but failed in reciprocal crosses with C. linearis `Bubba' and `Burgundy Lace'. To increase recovery of triploids, germination of triploid and tetraploid embryos was investigated, as either intact ovules or excised embryos, on Schenk and Hildebrandt (SH) basal salts supplemented with sucrose at 20, 40, and 80 g·L-1, presence or absence of 2% coconut-water, and gibberellic acid (GA3) at 0, 1, 2, or 4 μm, and harvested weekly beginning 2 weeks after pollination (WAP). Germination of triploids (cytochimera ×Chitalpa × diploid C. bignonioides) and tetraploids (selfed cytochimera ×Chitalpa) were greatest with excised embryos at 7 WAP on SH supplemented with sucrose at 20 g·L-1 and ≥1 μm GA3. Germination of triploids (diploid C. linearis × cytochimera ×Chitalpa) was &lt;5% at 4, 5, or 6 WAP on the same medium as above. Oryzalin effectively induced polyploidy and restored fertility in ×Chitalpa `Pink Dawn'. Successful crosses between hybrid and parental taxa of different ploidy levels, coupled with embryo culture will facilitate a ×Chitalpa breeding program. Chemical names used: 4(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin).

Molecular Confirmation of Intergeneric Hybrid ×Chitalpa tashkentensis (Bignoniaceae)

Intergeneric hybrids are generally rare; nevertheless, such putative hybrids need confirmation from other lines of evidence besides morphological intermediacy. In this study the authors used DNA sequences of nuclear and chloroplast genes to determine the hybrid identity of ×Chitalpa. Their results confirm that both ×Chitalpa tashkentensis `Pink Dawn' and ×C. tashkentensis `Morning Cloud' are the result of an Chilopsis linearis ×Catalpa sp. cross. However, Catalpa bignonioides does not seem to have participated in the cross, as speculated before. Different species of Catalpa may have been used as the paternal parent. ×C. tashkentensis `Morning Cloud' is the result of the C. linearis × C. speciosa cross, whereas the paternal parent of ×C. tashkentensis `Pink Dawn' may be a hybrid plant of C. ovata and C. speciosa.

The effect of spatial resolution on measurement of vegetation cover in three Mojave Desert shrub communities

Moderate resolution remotely sensed imagery (20–30 m) has lacked sufficient spatial resolution to accurately measure total vegetative cover in arid environments because the density of plant cover is generally too low to significantly influence spectral reflectance. New and emerging imagery is now available at significantly higher spatial resolutions, resulting in pixel sizes equal to or smaller than many dominant desert shrubs. This had led to an opposing problem, where desert shrubs now exhibit multi-modal probability functions associated with the individual elements of the plant, such as foliage, woody stems and branches, and shadows within and around shrub canopies. High resolution imagery was collected at three spatial resolutions for study sites in the south-central Mojave Desert of California to (1) determine the effect of spatial resolution on the detection of four common species of shrubs ( Chilopsis linearis, Psorothamnus spinosus, Larrea tridentata, and Ambrosia dumosa), (2) assess the affect of increasing pixel size on the accuracy of area estimates of shrub cover, and (3) assess the accuracy of vegetation cover measurements when compared to vegetation cover measured in the field. Spatial resolution greater than 1.0 m was not capable of discerning a large percentage of the shrubs in this region of the Mojave Desert. Yet, high correlation ( r 2 = 0.71 – 0.93 ) was found between field measurements of percent cover and those derived from imagery at spatial resolutions ranging from 0.6 to 1.0 m. The results indicated that a spatial resolution of 1.0 m or smaller was necessary to estimate percent cover and the area of individual shrubs from high-resolution imagery. Spatial resolution is dependent on the abundance and size of species of desert shrubs within plant communities, however 1.0 m resolution was found to be adequate for this region of the Mojave Desert.