3. Galium L. (bedstraw, cleavers)

Plants annual or perennial herbs, rarely woody at the base, the rootstock usually slender, sometimes reddish-tinged. Stems usually 4-sided, erect to loosely ascending, sometimes matted or clambering, sometimes notably hairy, roughened, and/or minutely prickly. Leaves in whorls of (3–)4–8(–12), rarely opposite at a few of the nodes, sessile or nearly so. Stipules absent. Inflorescences terminal and/or axillary, of solitary flowers or in clusters or panicles, not in headlike clusters subtended by involucral bracts. Flowers sessile or stalked, some of the flowers sometimes imperfect or sterile (mixed with perfect ones). Calyces essentially absent, occasionally represented by a minute rim at the flower base. Corollas 0.5–2.0 mm long, with a minute tube, deeply (3)4-lobed, the lobes spreading, not overlapping in bud, variously white, yellow, dark reddish purple, maroon, or yellowish green. Stamens (3)4, attached in the corolla tube, the anthers exserted. Style 2-lobed, the stigmas 2, capitate. Ovary inferior, 2-locular, the ovules 1 per locule. Fruits rather small (1–3 mm long), 2-lobed, dry (fleshy elsewhere), glabrous to tuberculate, sometimes densely pubescent with hooked hairs, separating into 2 indehiscent mericarps at maturity, these subglobose or less commonly broadly kidney-shaped. About 400 species, nearly worldwide, most diverse in temperate regions.

The Eurasian genus Asperula L. is very closely related to Galium (or perhaps not distinct), differing only in its trumpet-shaped corollas with well-developed tubes. The Eurasian species A. odorata L. (G. odoratum (L.) Scop.; sweet woodruff, waldmeister), is commonly cultivated as an ornamental groundcover, including in Missouri, and is similar in general aspect to G. circaezans. Asperula odorata has white flowers with a sweet, pleasant aroma, and in Europe is also used to flavor drinks, including May wine (Rombauer and Becker, 1975).

Readers should beware of confusing Galium with Mollugo (Molluginaceae). Although the flowers and inflorescences of the two genera are very different, both are weak-stemmed plants with whorled, relatively slender leaves. The development of the whorled, apparently nonstipulate leaves of Galium and a few related Rubiaceae genera (Rubia L., Sherardia) has been debated. The whorled leaves are distinctive for their lack of stipules (in a family otherwise characterized by the presence of stipules) and their arrangement commonly in even numbers. The leaves are sometimes considered actually to be produced in pairs, as in most other Rubiaceae, and the interpetiolar stipules in this case to be present and to have expanded to appear similar to the leaves, thus producing an apparent whorl of four leaves at each node. The leaves that are supposed to be derived from enlarged stipules cannot be separated from the true leaves, at least by an observer of the whole plant. In species with more than four leaves at a node, either more “true” leaves are assumed to have been produced, or the leaf-like stipules are thought to have become divided into several equal segments.

Galium generally has not been studied well in North America. Its taxonomy is complicated by the variability of the plant size, leaf size and shape, and development of the inflorescences within a single species, and also by the varied and perhaps variable breeding system of some species. Species of Galium range from occasionally with all the flowers perfect through polygamous to fully dioecious; so the flowers may be variously staminate, pistillate, perfect, or even completely sterile, all on one plant. The presence of hooked hairs on the fruits and ovaries has been considered informative taxonomically and is apparently consistent within at least most of the species that occur in Missouri. When these hairs are present, they are usually visible on the ovaries of the flowers as well as the fruits. The number of leaves at a node is also generally consistent for many species, such as G. circaezans, although it is quite variable in others, such as G. aparine. Leaf size may be widely variable, among plants but also along a single stem, which often shows a marked increase in size in the later-season leaves at the top of the stem. Most of the species have short, curved, sharply pointed hairs with stout bases; these have been described as prickly or rough; their orientation varies on different parts of the plant. Some of the species also possess embedded glands, which appear as small lines or streaks on the undersurface of the leaf blades. Soft or fine (nonprickly) hairs are also present in some species. The taxonomy of Galium is also complicated by the circumpolar distribution of some species (or groups of closely related species), so that plants from all three continents must be studied together to make sense of a given species.

Measurements of leaves given below include the smaller leaves at the stem bases; some other authors give leaf measurements only for the largest leaves on a stem, which should be kept in mind when comparing different treatments of Galium. Also, fruit size is given by some authors only for the individual mericarps of the fruit, at least for species with dry fruit; here the fruit size is that of the whole fruit, that is, of the paired mericarps when they are apparently mature. However, fruit measurements here are only for the fruit itself, not including any hairs. Occasionally only one of the two mericarps develops, and in this case the single mericarp is often a bit larger than those of a pair. Measurements given here of corollas report the length from the corolla base to the tips of the lobes; some other authors have given measurements of Galium flowers (but not those of other Rubiaceae) in terms of the diameter of the open flower.

Plants of some Galium species have a persistent sweet odor when dried, and in olden times were mixed with bedding to freshen it; G. boreale was one species used in this way, which is apparently the origin of the common name bedstraw. Other species, such as G. verum, were added to milk to curdle it. The hooked hairs of the fruits cause them to adhere to animal fur or clothing, apparently for dispersal. Even the vegetative portions of some species, for example G. aparine and G. asprellum, are sticky in this way, due to small spinules on their surfaces, and the whole plant can adhere to clothing or climb on other plants in this manner. This surface stickiness is apparently the origin of the common name cleavers (meaning cleaving to or sticking to). The flowers are varied in their pollinators and attractive mechanisms; they may be nearly odorless (to us), or sweetly fragrant, or in some fly-pollinated species may offer odors that only those insects can truly appreciate.