You know when you touch a thorny weed because it hurts! But technically, botanists identify those “thorns” on weeds as spines or prickles. They not only give gardeners pause, but also help protect plants from animal damage. Thorns, spines, and prickles appear on different plant parts and can help with identification.
- Spines are modified leaves, leaflets, petioles, or stipules. Think cactus or thistles.
- Prickles are modified epidural (outer) cells found on blackberry, raspberry, and rose stems.
- True thorns are modified stems or branches—like those on honey locust trees (Gleditsia triacanthos)—that are long, wicked-looking things, capable of serious damage.
To gardeners who get their fingers stuck while weeding, it matters not if that weed has spines, prickles, or thorns. It still hurts!
Weeds that stick and prick
Common cocklebur (Xanthium strumarium) is a native summer annual. It has alternate, triangular leaves and the stems have spots ranging from maroon to black. The oval shaped fruit (bur) is covered with spines. Burs start out green and turn brown in the fall. Each bur has two seeds—one growing the first year, with the second seed growing the next year. Cockleburs are spread by the burs hitching rides on animals and humans. They can be found in fields, roadsides, and wasteland.
Burrweed or spurweed (Soliva sessilis) is an annual winter weed found in lawns, mostly along the coast and in Piedmont N.C. It has low ferny foliage and sharp, spiny seed pods that ripen in spring and hurt your feet if you step on them barefoot. It is an early source of food for honey bees and other pollinators.
Spiny sowthistle (Sonchus asper) is a summer annual weed with deeply notched and wavy leaves with sharp spines on leaf margins. The young plant is a basal rosette (leaves radiating from the base of the stem and usually close to the ground). Older plants have an upright flowering stem (yellow flowers). It flowers in late spring into summer. It has alternately arranged oval leaves. Crushed leaves or stems produce a milky white latex. It is found in lawns, waste areas, and roadsides.
Perennial catbrier or greenbrier vines (Smilax) include some of the “ouchiest” of weeds you may face here in Western North Carolina. These are native vines that are desirable wildlife food—rabbits eat the new shoot, deer browse the leaves, and birds eat the fruits—but may not be welcome in your garden.
Thistles (Cirsium) are members of the Asteraceae (aster) family and are native to North America, Europe, and Western Asia. The European invasive bull thistle (Cirsium vulgare) is found throughout the United States and Canada.
What to do?
While these weeds mostly show up in pastures, agricultural fields, and roadsides, they can invade the garden. When dealing with any of these “ouchy” plants, it is best to wear thick gloves and approach with caution. Control vines by digging the tubers or rhizomes. Repeated cutting back and applying a drop of herbicide to the cut stem are also effective. Maintain a layer of mulch in the garden to retard weed growth. Scout for and manually pull weeds when they are small and especially when the ground is soft after a rain.
Article written by Kay Green, Extension Master GardenerSM Volunteer.