Many plants have developed methods of protecting their seeds from predators. Tough or spiny seed pods are some of the most common means of protecting seeds. These kinds of seed pods include a number of common weeds, such as Jimson weed, milkweed, cocklebur and puncturevine. In addition to their spiny seed pods, several of these plants are highly toxic and can be dangerous for both humans and grazing animals.
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Common milkweed, or Asclepias syriaca, is native to North America, though it has been introduced into Europe. A perennial weed, this plant springs up in clumps and patches throughout meadows, along fences and beside roadways every year. Milkweed plants have long stems that grow 2 to 6 feet tall, and they produce purple flowers and teardrop-shaped seed pods. Immature seed pods are green and spiny; but as they mature, they turn brown and split open to release myriad seeds attached to bits of silky material designed to catch the wind.
Datura stramonium, known by the common name Jimson weed, is an annual that blooms in spring and summer. This plant has long, flat leaves and produces funnel-shaped flowers that range in colour from white to pale violet. Jimson weed produces oval-shaped seed pods covered in tiny spines designed to ward off predators. In mid to late summer, the seed pods mature and open to release round, flat seeds. Jimson weed is toxic to both humans and animals, and ingestion of this plant can cause hallucinations and, in severe cases, coma or death.
Cocklebur, also called Xanthium strumarium, is common throughout the United States in crop and pasture land. This plant can grow as tall as 6 feet, and it produces myriad egg-shaped burs that are covered in tiny hooked bristles. Each burr contains two seeds that grow at different rates, one during the first year and the other in the year following. If ingested, this plant is poisonous to livestock and may cause vomiting, respiratory distress and possibly death. The seed oil from the cocklebur can be ingested by humans and is often used medicinally and for making yellow dye.
Puncturevine, also called devil's thorn and tackweed, goes by the scientific name Tribulus terrestris. This weed shows up in the late spring through early summer, along roadsides, in crop lands and waste areas. Puncturevine grows outward from a root crown and produces stems that are orange-brown in colour with bright yellow flowers. Each flower produces a five-rayed fruit covered in spines that turns brown as it matures and eventually splits into five separate seed pods. Each pod contains between two and five seeds and is protected by two large spines.
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