Silphium perfoliatum, the cup plant or cup-plant, is a species of flowering plant in the family Asteraceae, native to eastern and central North America. It is an erect herbaceous perennial with triangular toothed leaves, and daisy-like yellow composite flower heads in summer. The specific epithet perfoliatum means "through the leaf." There are two varieties:
Silphium perfoliatum var. connatum Silphium perfoliatum var. perfoliatum.
Common names
Description
Habitat and distribution
Silphium perfoliatum grows in sandy moist bottom lands, floodplains, near stream beds, in or adjacent to open woodland. Currently, it can be found in the following states:
USA (AL, AR, CT, GA, IA, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, NC, ND, NE, NJ, NY, OH, OK, PA, SD, TN, VA, VT, WI, WV) CAN (ON, QC) Silphium perfoliatum is listed as a threatened species in Michigan, while it is listed as a prohibited and highly invasive plant species in New York State.
Morphology of the plant The typical height of S. perfoliatum plant ranges from 1–2.5 m (3–8 ft). The stem is stout, smooth, slightly hairy (glabrous) strongly 4-angled square, like mint plants. The leaves are opposite, toothed and ovate. The petioles are widely winged and fused around the stem, forming a cup. The first flower develops on the tip of the main stem, then more flowers develop on side branches.
Morphology of the flowers The flowers, which appear from midsummer to autumn (fall), look very similar to sunflowers, but are a lot smaller; measuring about 2.5 cm in diameter, with golden yellow ray florets. In the middle of the flower there are small, sterile, tubular disk florets, which are structurally bisexual, but the stamens are the only fertile part, and they do not produce seeds. The corollas are tubular, 5-toothed, and the style is undivided.
Generative reproduction
The ray florets have female characteristics, and eventually develop to become thin brown achenes with a marginal wing utilized for wind dispersal. Insect pollinators including bees, butterflies, and skippers help to cross-fertilize flowers to produce seeds. 20 to 30 seeds are created in each flower head. Each seed is about 9 to 15 mm long, 6–9 mm wide, flattened in shape, with a thickness of 1 mm.
Vegetative reproduction Silphium perfoliatum is able to establish colonies due to its central taproot system and shallow rhizomes. A multi-rhizomed clone originating from a single seed is believed to be 15 years old. The roots found in botanical gardens have been estimated to be more than 50 years old. S. perfoliatum has an extensive root system and does not transplant well except when very young.
Habitat and hardiness Silphium perfoliatum's metabolic pathway is the C3 carbon fixation. This plant is highly adapted to endure extreme weather and inhospitable conditions. For example, during the winter, the roots remain dormant and can survive temperatures as low as −30 °C (−22 °F). Its optimal growing temperature is 20 °C (68 °F).
Uses
Use as energy crop Silphium perfoliatum is considered a potential energy crop plant, especially because it has low demands on the climate, the soil and previous crop and produces high amounts of biomass. Based on the results of the Thuringian State Institute of Agriculture the plant can be an alternative plant for biogas production. The annual biomass yields are very different according to the present literature: In the second cultivation year S. perfoliatumcan grow from 13 to 20 tons of biomass per hectare, an experiment done in Thüringen, Germany even showed that 18 to 28 tons of dry weight per hectare are possible.
Cultivation In Germany, the arable cultivation of S. perfoliatum is becoming increasingly widespread for biogas production. Its invasive potential for Mid European countries is considered low, but a spread through wind, birds and harvesting machines is possible. One has to be especially careful when growing S. perfoliatum near moving bodies of water, so that it cannot spread and germinate on river banks like Buddleja davidii does. This could be a potential problem, as these ecosystems are very sensitive.
Sowing and planting Due to low germination rate of 15–20% with untreated seeds S. perfoliatum is usually planted as seedling. This is the reason for high investment costs in establishing the crop. Furthermore, there is no yield in the first planting season as S. perfoliatum is only harvested from the second year on. In Germany, seeding time to obtain an acceptable seedling development is in the beginning of May. The highest biomass yield is achieved with 10 cm × 50 cm (within-row spacing: 10 cm; distance between the rows: 50 cm). In European climate conditions the planting of seedlings is typically carried out at the end of May, or the beginning of June with planting machines from the vegetable and gardening industries. Low plant density (50 cm × 75 cm, 75 cm × 75 cm) can give a higher yield in the first harvestable year compared to the higher plant densities (50 cm × 50 cm). In the second harvestable year, they are similar, regardless of the plant density. In order to avoid reduced yields in the first year a possible solution could be sowing S. perfoliatum in combination with corn. Three quarters of usual corn yields can be achieved in the first year and S. perfoliatum can establish after corn harvest, achieving its full potential in the following year.
Fertilisation The fertilisation of S. perfoliatum should take place as early as possible in the year. This minimizes damage to the lap shoots from driving over them. S. perfoliatuma needs about 1 kg N to form 1 dt of dry matter. Depending on the expected yield, the fertilization per vegetation period is 130 – 160 kg N/ha. The fertilization of the following nutrients also depends on the expected yield. With an expected yield of 150 dt/ha, S. perfoliatum requires the following quantities of nutrients:
Phosphorus: 25 kg/ha Potassium: 150 kg/ha Magnesium: 50 kg/ha Calcium: 200 kg/ha Other tests show that fertilization is no longer necessary from the second year onwards. This shows that fertilization depends strongly on the expected yield. With a higher weighting of the ecological effects of the crop, the fertilization can be omitted. When used as an alternative to corn (biogas production), the aim is to achieve the highest possible biomass yield and fertilization is therefore necessary.
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