Glechoma hederacea (syn. Nepeta glechoma Benth., Nepeta hederacea (L.) Trevir.) is an aromatic, perennial, evergreen creeper of the mint family Lamiaceae. It is commonly known as ground-ivy, gill-over-the-ground, creeping charlie, alehoof, tunhoof, catsfoot, field balm, and run-away-robin. It is also sometimes known as creeping jenny, but that name more commonly refers to Lysimachia nummularia. It is used as a salad green in many countries. European settlers carried it around the world, and it has become a well-established introduced and naturalized plant in a wide variety of localities.
It is considered an aggressive invasive weed of woodlands and lawns in some parts of North America.
Glechoma hederacea can be identified by its round to reniform (kidney or fan shaped), crenate (with round toothed edges) opposed leaves 2ñ3 cm (0.79ñ1.18 in) diameter, on 3ñ6 cm (1.2ñ2.4 in) long petioles attached to square stems which root at the nodes. The plant spreads either by stolon or seed, making it exceptionally difficult to eradicate. It is a variable species, its size being influenced by environmental conditions, from 5ñ50 cm (2.0ñ19.7 in) tall.
Glechoma is sometimes confused with common mallow (Malva neglecta), which also has round, lobed leaves; but mallow leaves are attached to the stem at the back of a rounded leaf, where ground ivy has square stems and leaves which are attached in the center of the leaf, more prominent rounded lobes on their edges, attach to the stems in an opposite arrangement, and have a hairy upper surface. In addition, mallow and other creeping plants sometimes confused with ground ivy do not spread from nodes on stems. In addition, ground ivy emits a distinctive odor when damaged, being a member of the mint family.
The flowers of Glechoma are bilaterally symmetrical, funnel shaped, blue or bluish-violet to lavender, and grow in opposed clusters of two or three flowers in the leaf axils on the upper part of the stem or near the tip. It usually flowers in the spring.
Glechoma thrives in moist shaded areas, but also tolerates sun very well. It is a common plant in grasslands and wooded areas or wasteland. It also thrives in lawns and around buildings since it survives mowing. Part of the reason for its wide spread is its rhizomatous method of reproduction. It will form dense mats which can take over areas of lawn and woodland and thus is considered an invasive or aggressive weed in suitable climates where it is not native.
A number of wild bees fly upon this plant, including Anthophora furcata, Anthidum manicatum, Anthophora plumipes, Anthophora quadrimaculata, Osmia aurulenta, Osmia caerulentes, and Osmia uncinata. The plant is also galled by several insects, including Rondaniola bursaria (Lighthouse Gall), Liposthenes glechomae or Liposthenes latreillei (Kieffer, 1898) (a gall wasp). Despite its name, it is not related to true ivy (Hedera).
Glechoma hederecea is gynodiecious, with genets being either female or hermaphrodite. The females depend upon pollen from hermaphrodites for pollination. Female flowers tend to be smaller than hermaphrodite flowers. There is disagreement among biologists as to whether hermaphrodite flowers can pollinate themselves. The plant spends the winter as either a small ramet or a small rosette. It produces flowers between April and July, which are visited by many types of insects, and can be characterized by a generalized pollination syndrome. Each pollinated flower can produce up to four seeds, which are dispersed by the stem bending over and depositing the ripe seeds in the ground adjacent to the parent plant, although ants may carry the seeds further. The seeds germinate a few days after contact with moisture, although they can be stored dry. Dry storage for a period up to a month is thought to improve the germination rate.
The plant can also reproduce clonally, with the stems bending down to the earth and allowing roots to attach themselves. Single clones can grow several metres across, although precise data is not currently available.