Asclepias meadii
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Asclepias meadii |
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| Torr. ex A. Gray |
Asclepias meadii is a species of silk plants ( Asclepias ) from the subfamily of silk plants (Asclepiadoideae). The specific epithet honors the doctor and botanist Dr. Samuel Barnum Mead, who first introduced the species in 1846, still under the name " Asclepias cordatum non Walt.?" described. John Torrey soon realized that it was a new species, which he named in honor of the first discoverer.
features
Vegetative characteristics
Asclepias Meadii is a perennial , herbaceous plant , tall (56 cm diameter) with simple, 31 to 92 cm, cyan, bare, coated with a white waxy substance stems . There is a long, white taproot. Usually only one stem is formed per rhizome from the middle to the end of April, more rarely several. They contain a white milky juice . The leaves, which are also coated with a white, waxy substance, are opposite and sessile. The simple leaf blade is with a length of 5 to 7 cm and a width of 1 to 5 cm or a length of about 7.5 cm and a width of 3.3 cm wide-oval to ovate-lanceolate with a pointed or also obtuse end and a broadly rounded or obtuse-angled base. They are tightly membranous to slightly succulent , blue-green and glabrous. A total of (only) three to seven leaf pairs (four to eight leaf pairs) are formed. The leaf veins form a herringbone pattern.
Inflorescence and flowers
The individually standing terminal, pendulous, flat to disc-shaped, dold-like inflorescences contain a few to several (6 to 23, mean 12 or 1 to 26, mean 12) flowers. The drooping inflorescences are caused by a hook-shaped appendage at the end of the 5 to 8 cm long inflorescence stem, a feature that has so far only been observed in Asclepias meadii . The flower stalks are rather thin and 1 to 1.5 cm long.
The flowers are fragrant and produce plenty of nectar. The five-fold flowers are relatively large and change their color from green to ivory during anthesis , when the flowers turn light cream in color. The five sepals are oblong-triangular and 3 to 5 mm long. The five corolla lobes are 7 to 9 mm long. The gynostegium, which sits on a very short, conical, approximately 1.5 mm high and 2.5 mm thick stem, is also greenish-cream in color. The corolla lobes are hood-shaped and very broad-oval with a length of 1.5 mm and a width of 2.5 mm. The interstaminal corolla lobes are fused, curved and sickle-shaped at the base. They are slightly shorter than the staminal corolla lobes. The tapered stylus head, cut off at the top, is about 2 mm high and 3 mm in diameter at the base.
Fruits and seeds
The follicles, which are bare on the outside, stand upright on stems bent downwards. They are slender-spindle-shaped, 8 to 10 cm long (11 to 12 cm) and about 1 cm thick. A follicle fruit contains 42 to 92 seeds (mean 60 seeds). The seeds are broadly oval, 8 mm long and have a white head of hair about 4 cm long.
ecology
The growth is relatively slow; even under ideal conditions they need four or more years to flower for the first time, in the wild they probably even take up to 15 years. The plants are very long-lived; proven to be over 25 years of age. They are probably well over 100 years old. They are very resistant to drought and probably also to pest infestation. Such stress events can cause the plant to die off completely, except for the rhizome. They do not sprout again until the following year or even the year after that. In doing so, they revert to their juvenile state, and it can again take years before inflorescences (and possibly seeds) are produced again.
Asclepias meadii flowers from May to June, usually the last week of May to the third week of June. A flower is open for five to six days. The flowers are pollinated by fur bees ( Anthophora species) and bumblebees ( Bombus species). Apparently cross-pollination occurs almost exclusively, self-pollination does not produce any germinable seeds. Cross-fertilization within a population of clones also does not result in germinable seeds. Even in genetically different populations, only a little over 6% of the flowering plants later also produced seed pods. Usually only one fruit was formed per flower, more rarely two fruits. The maturation period is 100 to 110 days; the seeds are ripe from the end of August to the beginning of September. Under laboratory conditions, the germination rate was relatively low at less than 50%.
Occurrence
The range of Asclepias meadii is currently limited to the US states of Wisconsin , Illinois , Indiana , Iowa , Missouri, and Kansas . However, Asclepias meadii had been more widespread and much more common in the recent past. Presumably it was originally quite common in the still untouched high grass prairies from northwest Indiana, southern Wisconsin and northern Iowa to southern Illinois, southern Missouri and northeastern Kansas. With the cultivation of the prairies, the species quickly disappeared and was already rare during Samuel Mead's lifetime, as he wrote in a letter in 1871. The current range is also due to reintroduction measures, because the species had already disappeared in Wisconsin and Indiana. In 1989 Illinois and Iowa had only small populations in two counties each.
Asclepias meadii basically grows in two somewhat different habitats , in dry high grass prairies and pristine prairies as well as on slopes with acidic, nutrient-poor, silicate-igneous rocks, but also nutrient-rich, calcareous soils . It is (still or again) widespread, but very rare. There are currently around 150 to 170 locations known. However, many locations are at risk because they are on private land and used for agriculture.
Pests
Asclepias meadii is harmed by some species of beetles. The larvae of Tetraopes femoratus ( longhorn beetles , Cerambycidae) and Rhyssematus species ( weevils , Curculionidae) feed on the roots of the plants. The adult Tetraopes femoratus have been observed eating the petals. The adult weevils prick the inflorescence shafts, which in extreme cases snap off and die. Asclepias meadii is also a food plant for the caterpillars of the monarch butterfly ( Danaus plexippus ). However, Asclepias meadii is rarely used compared to other silk plants.
Danger
Asclepias meadii is considered very endangered. In total, only about 150 locations are known. However, there are probably only a few survivable populations left . Many populations consist of only a few plants, some seem to be clones, since the species can also reproduce vegetatively to a small extent through rhizome runners. However, such populations cannot reproduce sexually, since self-fertilization rarely produces germinable seeds. They usually rely on cross-pollination to produce germinable seeds.
The main reason for the sharp decline was the cultivation of the fertile soils of the high grass prairies as early as the 19th century. Less fertile soils were used as hay meadows. The species has survived in a few protected areas of the high grass prairies and the hay meadow prairies. Here they are especially endangered by the annual mowing that takes place before the seeds mature and spread. The plants can no longer reproduce generatively and the plants on these hay meadows become too old, the populations decrease over the years. Presumably, these are plants that grew there before the hay meadow prairies were used and that have survived to this day. It was also found that the seeds germinate better if the high grass prairies are burned regularly. Failure to burn it reduces the species' chance of survival because the areas are overgrown by bushes and trees. Other factors include the destruction of habitats through overbuilding, through the use of herbicides that are applied directly (e.g. along railway lines) or blow over from neighboring, intensively used areas, and hikers who trample the plants. It was also found that the pollinators have decreased significantly. Theft or excavation can also noticeably damage one of these often very small populations.
Phylogeny
According to the phylogenetic analysis by Fishbein et al. (2011), based on non-coding chloroplast DNA sequences, Asclepias meadii is the sister species of Asclepias tomentosa .
swell
literature
- Robert E. Woodson, Jr .: The North American Species of Asclepias L. , In: Annals of the Missouri Botanical Garden , 41 (1), St. Louis, Mo., 1954, pp. 1-211 URL
- W. Dean Kettle, Helen M. Alexander, Galen L. Pittman: An 11-Year Ecological Study of a Rare Prairie Perennial (Asclepias Meadii): Implications for Monitoring and Management. , In: American Midland Naturalist , 144 (1), 2000, pp. 66-77 JSTOR-URL
Individual evidence
- ↑ a b c d e f g Mead’s Milkweed (Asclepias meadii) Recovery Plan (PDF; 2.3 MB)
- ^ Asclepias meadii - Torr. ex Gray
- ↑ a b Woodson (1956: pp. 109–110)
- ↑ a b c d e f g h i Robert F. Betz: Ecology of Mead's Milkweed (Asclepias meadii Torrey). Proceedings of the Eleventh North American Prairie Conferences, pp. 187-191, University of Nebraska, Lincoln, 1989. PDF
- ↑ a b c d e Center for Plant Conservation National Collection Plant Profile ( Memento of the original dated December 15, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ USDA Plants Profile
- ↑ Mark Fishbein, David Chuba, Chris Ellison, Roberta J. Mason-Gamer, Steven P. Lynch: Phylogenetic Relationships of Asclepias (Apocynaceae) Inferred from Non-coding Chloroplast DNA Sequences. In: Systematic Botany , Volume 36, No. 4, 2011, pp. 1008-1023 doi : 10.1600 / 036364411X605010
