Asclepias welshii
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Asclepias welshii |
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Asclepias welshii is a species of silk plants ( Asclepias ) from the subfamily of the silk plants (Asclepiadoideae). The specific epithet honors Stanley Larson Welsh , the former professor of botany and curator of the herbarium at Brigham Young University in Provo ( Utah , USA). The species is a pioneer plant on migrating sand dunes.
features
Vegetative characteristics
Asclepias welshii is a perennial , herbaceous , upright plant with a root system consisting of several tap roots that are connected by horizontal side shoots. The upright or ascending, strong shoots standing in clusters are 25 to 100 cm high (long) and are unbranched. The stalked leaves are opposite, the stems 1 to 5 mm (rarely up to 10 mm) long. The leathery leaf blades are shaped differently along the shoot. The upper leaves are broadly elongated-elliptical, ovate or obovate with a rounded or flattened, prickly-pointed outer end, and a rounded to approximately heart-shaped lower end. They are (6) 7 to 9 (15) inches long and (3) 3.5 to 6 (8) inches wide. The lower leaves are sessile, significantly smaller, elliptical with a pointed outer end and basal heart-shaped and encompassing stems. The leaves are initially densely covered with a white downy wool; they later become bald, especially on the underside.
The species forms three different types of shoots with corresponding leaf shapes, which are often formed by the same root system and can grow next to each other. Palmer & Armstrong refer to these different types as
- Primary stage with narrow, linear leaves. Seedlings and shoots that arise from smaller rhizomes and that can be several years old form this type.
- Secondary stage : intermediate forms between the primary stage and the mature stage
- mature stage : see above
Inflorescence and flowers
The few inflorescences sit laterally on the topmost nodes . They are stalked, the woolly hairy stems are 2 to 4 cm, rarely up to 7 cm long. The spherical, zymotic inflorescences have a diameter of 7 cm and contain up to 30, densely packed flowers. The comparatively large, stalked flowers are hermaphroditic, radial symmetry and five-fold. The stems are 8 to 13 mm (rarely up to 20 mm) long and woolly hairy. The sepals are already bent back at the base, then they curve upwards, following the curvature of the petals. They are linear, 5 to 7.5 mm long, green on top and woolly hairy on the underside. The corolla is cup-shaped with bent back and ascending petals. The very dense arrangement of the flowers in the inflorescence prevents the petals from spreading completely and forces them to rise. The corolla is (5) 6 to 7 (8) mm long, and cream-colored with a pink tint. The tips are egg-shaped, 6 to 7 mm long and have very fine hairs on the underside. The single-row staminal side crown is only very briefly stalked. The pale green stem is 0.5 mm long and 1.5 to 2.5 mm thick. The cream-colored, sack-shaped, rolled-up tips of the secondary crown are 2.5 to 4 mm long, the ends are broadly flattened and about 2 mm wide. They are about 1 mm longer than the gynostegium . The horn-shaped secondary process, which is flattened on the inside, attaches approximately to the middle of the inside of the tips and protrudes from the sack-shaped tips. It is sickle-shaped and curved almost horizontally over the stylus head . The stylus head is 1.2 to 1.5 mm high and 1.5 to 3.4 mm in diameter.
Fruits and seeds
The follicles stand splayed on splayed or hanging stems. They are broad-spindle-shaped and 4 to 7 cm long. The smooth or woolly hairy surface has soft, awl-like tubercles. The seeds are broadly elliptical and up to 20 mm long ( Roth (2001) ). The head of hair is only rudimentary.
Geographical distribution and (syn-) ecology
The species is only known from a small area on the border between the American states of Arizona and Utah . It grows there to 1700 to 1900 m. The largest and most individual occurrence is in Coral Pink Sand Dunes State Park in southern Utah.
Asclepias welshii is a pioneer plant that inhabits active, not yet overgrown sand dunes, along with Redfieldia flexuosa . The rhizome-like roots reach meters deep into the sand, possibly even into the surrounding rock. Several shoots can be formed from this widely ramified root system, which can often be located far apart, depending on the root system. It is therefore often difficult to determine how many (genetically) different individuals actually colonize a dune, or whether they are clones of the same plant. If a dune stabilizes and is colonized by other plant species, Asclepias welshii can ultimately be displaced. The reproduction takes place primarily vegetatively; but also by seeds. So that the seeds fall into a suitable habitat, the hairs of the seeds are only rudimentarily developed. The seeds are hardly transported by wind. When the seed capsule bursts, the seeds fall into the immediate vicinity of the parent plant.
In the dune landscape, Asclepias welshii is associated with Wyethia scabra , Artemisia campestris , Chrysothamnus nauseosus , Eriogonum alatum , Eriogonum leptocladon , Psoralidium lanceolatum , Calamovilfa gigantea and Muhlenbergia pungens . In the wider area there are also: Juniperus osteosperma , Pinus ponderosa and Quercus gambelii . The flowering period is from June to July, the seeds are formed from July to early September.
The following insect species have so far been identified as pollinators of the flowers:
- Ceratina nanula
- Xylocopa californica
- Western honey bee ( Apis mellifera )
- Bombus bifarius
- Dialictus albohirtus
- Dialictus ruidosensis
- Anthidium rodecki
- Heriades timberlakei
- Polistes dorsalis
- Mimesa sp.
- Microbembex californica
- Bembex americana
- Oxybelus californicus
- Euphydryas anicia
- Euxoa aurulenta
Taxonomy and systematics
The taxon was first described in 1979 by Noel Herman Holmgren and Patricia Kern Holmgren after an occurrence in Kane County in the American state of Utah . Since then, more deposits have been added in three counties in the state of Arizona. Synonyms are not known.
Danger
The area is endangered by off-road vehicles. The species is classified as Critically Imperiled or "Endangered".
supporting documents
literature
- Eric Sundell: Asclepiadaceae Milkweed Family. , In: Journal of the Arizona-Nevada Academy of Science , Vol. 27, No. 2, 1993, pp. 169-187. PDF (p. 181/2)
- Noel Herman Holmgren, Patricia Kern Holmgren: A new species of Asclepias (Asclepiadaceae) from Utah. In: Brittonia , Vol. 31, No. 1, 1979, pp. 110-114. [JSTORE]
- Daniela Roth: Species account for Asclepias welshii. Navajo Natural Heritage Program, PO Box 1480, Window Rock, AZ 86515 2001 PDF .
- Arizona Game and Fish Department: Asclepias welshii N. & P. Holmgren. Unpublished abstract compiled and edited by the Heritage Data Management System, Arizona Game and Fish Department, Phoenix, AZ. 6 pp., 2005 PDF
- BC Palmer, L. Armstrong: Demography and Monitoring of Welsh's Milkweed (Asclepias welshii) at Coral Pink Sand Dunes. Southwestern Rare and Endangered Plants: Proceedings of the Third Conference, September 25-28, 2000 Flagstaff, Arizona, pp. 59-69 PDF
- Patricia Kern Holmgren: PDF
- Lee E. Hughes: Monitoring Update on Four Listed Plants on the Arizona Strip. PDF
Individual evidence
- ^ Pollinator Conservation Digital Library
- ↑ Rafael Govaerts (ed.): World Checklist of Selected Plant Families (in review): Asclepias. Published in: The Plant List. A working list of all plant species. Royal Botanic Gardens Kew, Missouri Botanical Garden, accessed May 24, 2013.
- ↑ NatureServe Explore - Asclepias welshii
- ↑ Department of the Interior Fish and Wildlife Service 50 CFR Part 17 Rules and Regulations 41435 Endangered and Threatened Wildlife and Plants; Final Rule Determining Asclepias welshii (Welsh's Milkweed) To Be a Threatened Species With Critical Habitat. Federal Register , Vol. 52, No. 208, from October 28, 1987 PDF
