Eating Weeds: Cleavers Coffee

One of the world’s most beloved beverages comes from a species of plant found in the fourth largest family of flowering plants. Rubiaceae, also known as the coffee or bedstraw family, consists of around 13,500 species, placing it behind just Asteraceae, Orchidaceae, and Fabaceae for the most number of species. Coffea arabica, and other species in the genus Coffea, are grown for their fruits which are used to make coffee. This makes Rubiaceae one of the most economically important plant families. A family this size is bound to be home to a weed or two, and in fact, one of the most widespread and obnoxious weeds is also a member of Rubiaceae.

Galium aparine, known commonly by a slew of names including cleavers, occurs naturally across large portions of Europe, Asia, North Africa, and possibly even parts of North America. It has been introduced as a weed in many locations across North America, South America, Australia, New Zealand, Japan, and parts of Africa. It is of particular concern in agricultural settings where its lengthy, sprawling branches and sticky leaves get tangled up in harvesting equipment, while its tiny, prickly fruits get mixed in with seeds of similar size like canola.

Galium aparine

Sticky willy, as it is also known, is an annual plant that, in some cases, can have two generations per year – one in the spring (having germinated the previous fall) and one in the summer. Its stems are square, though not as sharply square as plants in the mint family, and can grow to around six feet long. They are weak, brittle, and don’t stand upright on their own; instead they are found scrambling across the ground or, when given the opportunity, climbing up the lengths of other plants in order to reach the sunlight. Leaves occur in whorls of six to eight and are simple and slender with entire margins. Flowers are produced at leaf axils along the lengths of the branches and are tiny, four-petaled, star-shaped, and greenish white. Fruits are borne in pairs and are round, single-seeded, indehiscent nutlets. The stems, leaves, and fruits are covered in stiff, hooked hairs or trichomes, earning it other names like catchweed bedstraw, grip grass, stickyweed, and velcro plant.

flowers and immature fruit on Galium aparine

Galium aparine is a climbing plant, but unlike other climbing plants, it doesn’t twine up things or produce structures like tendrils to hold itself up. Instead, its ability to climb is made possible by its abundant bristly hairs. A paper published in Proceedings of the Royal Society B (2011) investigates the way G. aparine climbs up other plants using the hairs on its leaves. A close inspection of the leaves reveals that the trichomes on the top of the leaf (the adaxial leaf surface) differ significantly from those found on the bottom of the leaf (the abaxial leaf surface). Adaxial trichomes curve towards the tip of the leaf, are hardened mainly at the tip, and are evenly distributed across the leaf surface. Abaxial trichomes curve towards the leaf base, are hardened throughout, and are found only on the midrib and leaf margins.

Having different types of hairs on their upper and lower leaf surfaces gives cleavers an advantage when it comes to climbing up neighboring plants. The authors of the paper describe the technique as a “ratchet mechanism.” When the upper surface of their leaf makes contact with the lower surface of another plant’s leaf, the flexible, outwardly hooked trichomes inhibit it from slipping further below the leaf and allow it to easily slide out from underneath it. When the lower surface of their leaf makes contact with the upper surface of another plant’s leaf, the stiff, inwardly hooked trichomes keep it attached to the leaf even if the other leaf starts to slip away and allows it to advance further across the leaf for better attachment and coverage. Using this ratchet mechanism, cleavers climb up the leaves of other plants, keeping their leaves above the other plant’s leaves, which gives them better access to sunlight. The basal stems of cleavers are highly flexible, which keeps them from breaking as the plant sways in the wind, tightly attached to their “host” plant.

fruits of Galium aparine

The hooked trichomes on the tiny fruits of cleavers readily attach to the fur and clothing of passing animals. The nutlets easily break free from the plants and can be transported long distances. They can also be harvested and made into a lightly caffeinated tea. Harvesting the fruit takes time and patience. I spent at least 20 minutes trying to harvest enough fruits for one small cup of cleavers coffee. The fruits don’t ripen evenly, and while I tried to pick mostly ripe fruits, I ended up with a selection of fruits in various stages of ripeness.

To make cleavers coffee, first toast the seeds for a few minutes in a pan heated to medium high, stirring them frequently. Next, grind them with a mortar and pestle and place the grinds in a strainer. Proceed as you would if you were making tea from loose leaf tea.

The toasted fruits and resulting tea should smell similar to coffee. The smell must not be strong, because my poor sense of smell didn’t really pick up on it. The taste is coffee-like, but I thought it was more similar to black tea. Sierra tried it and called it “a tea version of coffee.” If the fruits were easier to collect, I could see myself making this more often, but who has the time?

The leaves and stems of Galium aparine are also edible, and the plant is said to be a particular favorite of geese and chickens, bringing about yet another common name, goosegrass. In the book Weeds, Gareth Richards discusses the plant’s edibility: “It’s edible for humans but not that pleasant to eat; most culinary and medicinal uses center around infusing the plant in liquids.” Cooking with the leaves or turning them into some sort of spring tonic is something I’ll consider for a future post about eating cleavers.

More Eating Weeds Posts on Awkward Botany

The Wonderful World of Plantlets, Bulbils, Cormlets, Tubercles, and Gemmae

Probably the most well known strategy that plants have for dispersal is by way of seeds. Seeds are plants in embryo, and new generations of plants are born when seeds, released from their parent plants, find suitable locations to germinate. But one of the most amazing things about plants in general is that they have the ability to reproduce in a variety of different ways, and many plant species are not limited to seeds as their only means of dispersal. A paper by Scott Zona and Cody Coyotee Howard, published in Flora (February 2022), introduces us to the intriguing world of aerial vegetative diaspores – just one of the many ways that plants have to get around.

A diaspore is a plant structure that facilitates dispersal. Seeds are diaspores, as are spores, which are produced by non-seed bearing plants like mosses and ferns. If you’ve ever planted bulbs, you’ve handled another type of diaspore. Bulbs and corms, which many spring flowering plants are grown from, form little offshoots called bulblets and cormels that, when detached from their parent structure, can grow into new individuals. These vegetative diaspores are produced below ground. Aerial vegetative diaspores, on the other hand, are formed on above ground plant parts. This clunky term encompasses a number of different structures that are often simply called bulbils, which Zona and Howard explain is used as “a catch-all term that obscures their morphological identity.”

Compiling a list of plant species that feature aerial vegetative diaspores is a difficult task when plant descriptions from various sources use a broad selection of terminology for the same or similar plant parts. To help complete this task, Zona and Howard defined five distinct types of aerial vegetative diaspores – plantlets, bulbils, cormlets, tubercles, and gemmae – and came up with a list of 252 taxa that are known to feature at least one of these structures.

plantlets on the leaf margin of Kalanchoe daigremontiana (wikimedia commons; Aurélien Mora)

Plantlets are miniature plants attached to another plant. Once mature, they have clearly visible leaves, stems, and roots (or root initials) and are non-dormant, meaning they are ready to grow on their own as soon as they’re given the opportunity. The tiny plants borne along the margins of the leaves of mother of thousands (Kalanchoe daigremontiana) is a great example of a plantlet.

A bulbil consists of a shortened stem surrounded by scale leaves modified for food and water storage. Sometimes root initials are visible at the base of the bulbil. Bulbils remain dormant until they are dispersed and conditions are suitable for growth. When bulbils start growing but remain attached to the plant, they become a plantlet. A good example of a bulbil can be found on bulbous bluegrass (Poa bulbosa).

Cormlets are comprised of stem tissue and, like plantlets and bulbils, have a single axis of polarity. They have highly reduced scale leaves and are dormant at dispersal. Bulbil bugle lily (Watsonia meriana), despite its misleading common name, is a good example of a plant that produces cormlets.

Tubercles are made up of swollen stem tissue and, like tubers (their underground counterparts), have multiple shoot buds and multiple axes of polarity (meaning there is no right side up like there is in plantlets, bulbils, and cormlets). They lack scale leaves and are dormant at dispersal. Air potato (Dioscorea bulbifera) is an example of a tubercle-producing plant. As you might guess from the common name, potato-like structures are produced aerially on this vining plant that was introduced to North America from Africa and is now invasive in Florida.

A gemma is a tiny cluster of undifferentiated cells. Gemmae are non-dormant and lack polarity. They are the smallest and least common form of aerial vegetative diaspore and can be found on Drosera pygmaea, a species of sundew native to parts of Australia and New Zealand.

Drosera pygmaea (wikimedia commons; Björn S…)

Zona and Howard’s list of plants with aerial vegetative diaspores is the most comprehensive list to date – although it is undoubtedly and understandably missing some – and includes representatives from 42 plant families and 21 plant orders. Plantlets are the most common form of aerial vegetative diaspore at 116 taxa, with bulbils coming in second at 72. Cormlets and tubercles are less common, with 25 and 16 taxa respectively. Their paper includes the full list and offers further information about many of the species listed. It’s worth taking time to explore and is a valuable resource for anyone interested in the topic. In addition, their discussion section highlights a number of questions that warrant further investigation.

Questions surrounding reproductive strategies and the dispersal of aerial vegetative diaspores are particularly interesting. Because these structures are vegetative, they are essentially clones of the parent plant, meaning there is no genetic mixing as occurs when seeds are produced. This can be an advantage when sexual reproduction isn’t possible due to lack of pollinators, environmental restrictions, or chromosomal/polyploidy anomalies. It also assures that new individuals are pre-adapted to the site, and it can help a species colonize an area quickly. This ability to rapidly colonize explains why several of the species on Kona and Howard’s list are known to be invasive in parts of the world outside of their native range.

A species that produces both seeds and aerial vegetative diaspores may have an advantage when it comes to dispersal since both types of diaspores have their strengths. Seeds can remain dormant in the soil and are likely to persist in the environment longer than vegetative diaspores, but vegetative diaspores can be produced without relying on pollinators and can establish new individuals quickly. The modes of dispersal between the two can also vary. Seeds can be dispersed by wind or carried away by animals, while vegetative diaspores often rely solely on gravity to get around. One exception is hitchhiker elephant ear (Remusatia vivipara), whose bulbils are equipped with tiny hooks that cling to animal fur and are transported in a similar manner to burs.

hooked bulbils of hitchhiker elephant ear (Remusatia vivipara) (wikimedia commons; Dinesh Valke)

When the advantages of aerial vegetative diaspores are considered, it is a wonder that we don’t see them more often. Many plants can be easily propagated by taking stem, leaf, and/or root cuttings and placing them in conditions that favor adventitious root and shoot growth. This may suggest that dormant genetic pathways for producing vegetative diaspores exist in most plants. Or maybe not. Genetic studies of species that feature these structures are needed in order to understand why they are found in some species and not others. Kona and Howard leave us with a slew of research questions like this, and it’s a topic I’ll continue to check in on.

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