drought tolerance

by

Randomly Selected Botanical Terms: Glochids

The spines of a cactus are an obvious threat. They are generally sharp, smooth, and stiff; as soon as you are stabbed by one, it is immediately clear that you’ve gotten too close. Sitting at the base of the spines – or in place of spines – on many species of cacti is a less obvious, but significantly more heinous threat. Unless you’re looking closely, this hazard is practically invisible, and the pain and irritation that can come as a result of close contact has the potential to last significantly longer than the sharp poke of a spine. This nefarious plant part is called a glochid, and if you’ve ever made contact with one (or more likely several dozen of them), it’s not something you will soon forget.

Opuntia polyacantha x utahensis

The spine of a cactus is actually a leaf. The area from which a spine emerges from the fleshy, photosynthetic stem of a cactus is called an areole, which is equivalent to a node or bud on a more typical stem or branch from which leaves emerge. In place of typical looking leaves, a cactus produces spines and glochids. Like spines, glochids are also modified leaves, although they appear more like soft, little tufts of hair. However, this unassuming little tuft is not to be trifled with.

Close inspection of a glochid (with the help of a microscope) reveals why you don’t want them anywhere near your skin. While the surface of a cactus spine is often smooth and free of barbs, glochids are covered in backwards-facing barbs. The miniscule size of glochids combined with their pliable nature and retrose barbs, make it easy for them to work their way into your skin and stay there. Unlike spines, glochids easily detach from a cactus stem. Barely brushing up against a glochid-bearing cactus can result in getting stuck with several of them.

Opuntia basilaris var. heilii

Because glochids can be so fine and difficult to see, you may not even be aware they are there. You probably won’t even feel them at first. Removing them is a challenge thanks to their barbs, and since you may not be able to remove them all, the glochids that remain in your skin can continue to cause irritation for days, weeks, or even months after contact. For this reason, cactuses are generally best seen and not touched, or at the very least, handled with extreme care.

Apart from being a good form of defense, the glochids of some cactus species can serve an additional function. Most cactus species occur in arid or semi-arid climates, where access to water can be quite limited. In order to increase their chances of getting the water they need, some desert plants are able to collect water from the air. A few species of cactus do this, and glochids are a critical component in making this happen.

Cylindropuntia whipplei

A study published in the Journal of King Saud University – Science (2020) examined the dew harvesting ability of Opuntia stricta, commonly known as erect prickly pear. As described above, the spines of O. stricta are smooth, while the glochids are covered in retrose barbs. Both structures are waterproof due to hardened cell walls and cuticles. However, due in part to the conical shapes of both the glochids and their barbs, water droplets from the air are able to collect on the tips of the glochids. From there, the researchers observed the droplets in their travel towards the base of the glochids. As they moved downward, small droplets combined to form larger droplets.

At the base of the glochids are a series of trichomes, which are small hair-like outgrowths of the epidermis. The trichomes do not repel water, but rather are able to absorb the droplets as they reach the base of the glochids. For a plant species that receives very little water from the soil, being able to harvest dew from the air is critical for its survival, and this is thanks in part to those otherwise obnoxious glochids.

See Also: Prickles

Advertisement
by

Summer of Weeds: Eating Purslane

If it wasn’t so prolific and persistent, purslane would probably be a welcome guest in our vegetable gardens and edible landscapes. Easily among the most nutritious and versatile of the edible weeds, Portulaca oleracea is an annoyingly abundant annual that has inserted itself into garden beds and croplands in temperate climates across the globe. Thought to have originated in India or somewhere in Eurasia, purslane invaded North America long before Europeans did and has been naturalized across much of the continent for hundreds of years.

common purslane (Portulaca oleracea)

There are over 100 known species in the genus Portulaca, the only genus in the family Portulacaceae (otherwise known as the purslane family). Common purslane is a succulent plant with paddle- or teardrop-shaped leaves that generally grows low to the ground, forming a thick mat. It reaches for the sky when grown in shade or when competing with other plants for space. It produces little, yellow flowers that only open in bright sun and are typically self-pollinated. A small capsule containing dozens of tiny, black seeds quickly follows each flower. Each plant can produce tens of thousands of seeds, which remain viable for around 40 years.

Attempts to remove purslane by cultivation may only aid its survival. Broken pieces of the plant can take root in the soil, and uprooted plants can re-root if they are in contact with soil. Stirring up the ground brings to the surface seeds from purslane’s extensive seed bank. These freshly exposed seeds can then germinate, taking advantage of disturbance and open space. For all these reasons and more, John Eastman writes in The Book of Field and Roadside: “Purslane knows how to live and linger.”

The ever-urban and ever-common purslane.

The seeds of purslane germinate in late spring and throughout the summer when the soil has reached at least 75 – 80° Fahrenheit. It is adapted to high heat and dry soils. In order to conserve water, it switches to CAM photosynthesis when conditions are particularly hot and dry. In this photosynthetic pathway, carbon dioxide is stored as malic acid during the night and then converted back during the day. This means that, when it comes to eating purslane, the flavor changes depending on when the plant is harvested. In The Wild Wisdom of Weeds, Katrina Blair discusses this phenomenon: “In the morning purslane leaves contain as much as ten times more malic acid, making them very sour tasting. If you prefer a milder tasting purslane, harvest your greens in late afternoon and if you want more zing to your recipes, gather the leaves at dawn.”

Speaking of eating purslane, if all the claims are to be trusted, there may not be a more nutritious weed. In A Feast of Weeds, Luigi Ballerina calls it “a health bomb” because “it contains more omega-3 fatty acids than almost any other green, not to mention vitamins A, B, and C and beta carotene.” Blair calls it “one of the most nutritious plants on Earth,” and goes on to sing praises about its richness in dietary fiber, vitamins, minerals, protein, etc. Funnily enough, in describing the health benefits of purslane, Ballerina also quotes ancient sources claiming that “purslane calms sexual excitement.” Apparently it not only “eliminate[s] sensual dreams, but if used too much, it often extinguishes all ardor and even the capacity to procreate.”

With that caveat in mind, I tried it anyway. I had eaten it before, but nothing more than a leaf here and there and once in a green salad. I picked two recipes to try: Walnut Purslane Coleslaw from The Wild Wisdom of Weeds and Potatoes and Purslane from A Feast of Weeds. I’m generally a big fan of coleslaw, but for whatever reason I found this recipe to be a little bland. It was missing something, but I couldn’t put my finger on it. The purslane seemed to add a vague slimy-ness to it, which it will do on account of its mucilaginous nature.

Walnut Purslane Coleslaw

The Potatoes and Purslane recipe involved cooking the purslane. I enjoyed the finished product both hot and cold. The purslane added a sort of lemon-y spinach flavor. Those who tried it with me also liked it. The potato recipe was made with purslane that had been harvested in the morning, which may explain the strong lemon-y flavor. The coleslaw was made with purslane harvested in late afternoon, which may explain its blandness. I will have to try it the other way around for comparison. Purslane recipes abound in books and on the internet; browsing through them, I am intrigued enough to consider trying others. I think I’ll start with pickled purslane, purslane pesto, and perhaps, purslane sauerkraut.

Potatoes and Purslane

More Resources:

———————

Do you have a favorite purslane recipe? Share it in the comment section below.