Differential Morphology: Galiums Galore

Updated: May 8

Did you know that there are over 600 species of Galium, or Bedstraws, 60 of which exist in the U.S.? Galium aparine, commonly known as Cleavers, is by far the most well known and most utilized for herbal medicine. Galium has a long history of use in folk medicine as a spring alterative and kidney tonic. The presence of coumarins, which give certain species such as Galium triflorum (Fragrant Bedstraw) their scent, are natural blood thinners and promote lymphatic drainage. The name Galium is derived from the Greek word γάλα (GAH-la) meaning milk, pointing to a bit of its history, in which its juice was used to curdle milk.

Photo credit: Jaybird Tignor

There are 18 species present here in Pennyslvania, including several native ones, and contrary to popular belief G. aparine is also a native species. There are three species of Galium that are threatened in Pennsylvania, including Galium labradoricum (Bog Bedstraw), Galium latifolium (Purple Bedstraw), and Galium trifidum (Small Bedstraw).

Many other Galiums are mistaken for Cleavers, but luckily most species can be used analogously. Do you know how to tell Cleavers apart from other species? Of course its easier to tell when in flower, but there are many identifying characteristics to differentiate species in the very early spring, without flowers present.

Galiums are sprawling species, often reclining due to their weak stems. Their stems are square, but if you ever heard the caution "not all square stemmed plants are mints!" you may wonder what family they are in- for they certainly don't have opposite leaves. Galium is in the Madder Family, Rubiaceae, which is the same family that contains Coffee. Galiums are well known for their whorled leaves, which grow in size as they approach the terminus of the stem. Delicate flowers form in either branched terminal (with a bud occurring at the apex of the stem) and axillary (occurring the in junction of the leaf and stem) cymes (the central flower blooms first), or occasionally in axillary clusters.

This first image pictured here is Galium aparine, known Cleavers, Catchweed, or Stickyweed due to its abundance of what is probably the most well-recognized feature of Galium: downward pointing, barbed-like trichomes (hairs) that enable it to cling to nearly anything it comes into contact with. These barbs are enriched with pectins, giving them extra stability to act like a pseudovine, climbing without the need to climb or produce tendrils. Most folks familiar with this plant have experienced the initiation of tossing a bit of Cleavers onto a companion's shirt, resulting in twitters of glee when it infallibly sticks (I imagine Cleavers shares our excitement, given that its stickiness is a evolutionary adaptation to encourage dispersal). Rub your finger over Cleavers and it feels a lot likes a cat's tongue. About 50% of Galium species have this rough, bristly characteristic, though usually to a lesser extent.

Galium asprellum, or Rough Bedstraw is another common species with barbed trichomes. We can observe the number of leaves in a whorl to help us tell them apart. Galiums can have anywhere between 4-8 leaves per whorl. G. aparine has 6-8 leaves in a whorl. G. asprellum has 6, never 8, but occasionally 4-5 on branches. It also has slightly shorter, wider leaves. Another way to differentiate Rough Bedstraw from Cleavers in its post-flowering stage is to look at the fruits. Rough bedstraw has smooth fruits, whereas Cleavers fruits are rarely smooth, having hook bristles.

Galium triflorum, Fragrant Bedstraw, can be differentiated from G. aparine and G. asprellum by its antrorse barbs along the leaf margin, meaning they point forwa