Big Things Come In Small Packages

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Meet Blossfeldia liliputana, the smallest species of cactus in the world. With a maximum diameter of only 12 mm, this wonderful succulent would be hard to spot tucked in among the nooks and crannies of rock outcrops. Its species name "liliputana" is a reference to the fictional island of Liliput (Gulliver's Travels) whose inhabitants were said to be rather small. If its size alone wasn't interesting in and of itself, the biology of B. liliputana is also downright bizarre.

B. liliputana is native to arid regions between southern Bolivia and northern Argentina. It appears to prefer growing wedged between cracks in rock as these are usually the spots where just enough soil builds up to put down its roots. Root formation, however, does not happen for quite some time. Most often new individuals bud off from the parent plant. They emerge not from the base, but rather from apical tissues, yet another unique feature of this cactus. What's more, this cactus produces no spines. Instead, its numerous areoles are covered in a dense layer of trichomes that are rather felt-like to the touch.

As you can clearly see, this species is small. It only ever becomes conspicuous when it comes time to flower. Imagine a bunch of tiny white to pink cactus flowers poking out of a crevice. It must be a remarkable sight to see in person. Despite their showy appearance, its is believed that most are self-fertilized.

As mentioned, the size of this cactus isn't the only interesting thing about its biology. B. liliputana is categorized as a poikilohydric organism, meaning it doesn't have the ability to regulate its internal water content. Researchers have found that individual plants can lose up to 80% of their weight in water and can maintain that state for as long as two years without any negative effects. As such, colonies of these tiny cacti often appear shrunken or squished. Once the rains arrive, however, it springs back to its original rounded shape with seemingly no issues. Amazingly, a significant amount of water uptake happens via the fuzzy areoles that cover its surface, hence it does not harm the plant to hold off growing roots for quite some time. 

Speaking of water regulation, B. liliputana holds another record for having the lowest density of stomata of any terrestrial autotrophic vascular plant. Stomata are the pores in which plants regulate water and gas exchange so having so few may have something to do with why this species loses and gains water to such a degree that would kill most other vascular plant species.

Another peculiar quality of this cactus are its seeds. Unlike all other cacti whose seeds are hard and relatively smooth, the seeds of B. liliputana are hairy. Attached to each seed is a small fleshy structure called an aril, which aids in seed dispersal. As it turns out, B. liliputana relies on ants as its main seed dispersers. Ants attracted to the fleshy aril drag the seeds back to their nests, remove and eat the aril, and then discard the seed. This is often good news for the cactus because its seeds end up in nutrient-rich ant middens protected from both the elements and seed predators, often in much more suitable conditions for germination.

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Needless to say, B. liliputana is a bit of an oddball as far as cacti are concerned. Its highly derived features coupled with its bizarre biology has made it difficult for taxonomists to elucidate its relationship to the rest of the cactus family. It certainly deserves its own genus, to which it is the only member, however, it has been added to and removed form a handful of cactus subfamilies over the years. The most recent genetic analyses suggests that it is unique enough to warrant its own tribe within Cactaceae - Blossfeldieae.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Leafy Cacti?

Pereskia aculeata

Pereskia aculeata

At first glance, there is little about a Pereskia that would suggest a relation to what we know as cacti. Even a second, third, and forth glance probably wouldn't do much to persuade the casual observer that these plants have a place on cacti family tree. All preconceptions aside, Pereskia are in fact members of the family Cactaceae and quite interesting ones at that.

Most people readily recognize the leafless, spiny green stems of a cactus. Indeed, this would appear to be a unifying character of the family. Pereskia is proof that this is not the case. Though other cacti occasionally produce either tiny, vestigial leaves or stubby succulent leaves, Pereskia really break the mold by producing broad, flattened leaves with only a hint of succulence.

Pereskia spines are produced from areoles in typical cactus fashion.

Pereskia spines are produced from areoles in typical cactus fashion.

What's more, instead of clusters of Opuntia-like pads or large, columnar trunks, Pereskia are mainly shrubby plants with a handful of scrambling climbers mixed in. Similar to their more succulent cousins, the trunks of Pereskia are usually adorned with clusters of long spines for protection. Additionally, each species produces the large, showy, cup-like blooms we have come to expect from cacti.

They are certainly as odd as they are beautiful. As it stands right now, taxonomists recognize two clades of Pereskia - Clade A, which are native to a region comprising the Gulf of Mexico and Caribbean Sea (this group is currently listed under the name Leuenbergeria) and Clade B, which are native to regions just south of the Amazon Basin. This may seem superficial to most of us but the distinction between these groups has a lot to teach us about the evolution of what we know of as cacti. 

Pereskia grandifolia

Pereskia grandifolia

Genetically speaking, the genus Pereskia sorts out at the base of the cactus family tree. Pereskia are in fact sister to all other cacti. This is where the distinction between the two Pereskia clades gets interesting. Clade A appears to be the older of the two and all members of this group form bark early on in their development and their stems lack a feature present in all other cacti - stomata. Stomata are microscopic pours that allow the exchange of gases like CO2 and oxygen. Clabe B, on the other hand, delay bark formation until later in life and all of them produce stomata on their stems.

The reason this distinction is important is because all other cacti produce stomata on their stems as well. As such, their base at the bottom of the cactus tree not only shows us what the ancestral from of cactus must have looked like, it also paints a relatively detailed picture of the evolutionary trajectory of subsequent cacti lineages. It would appear that the ancestor of all cacti started out as leafy shrubs that lacked the ability to perform stem photosynthesis. Subsequent evolution saw a delay in bark formation, the presence of stomata on the stem, and the start of stem photosynthesis, which is a defining feature of all other cacti.

Pereskia aculeata

Pereskia aculeata

If you are as excited about Pereskia as I am, then you , my friend, are in luck. A handful of Pereskia species have found their way into the horticulture trade. With a little luck attention to detail, you too can share you home with one of these wonderful plants. Just be warned, they get tall and their spines, which are often hidden by the leaves, are a force to be reckoned with. Tread lightly with these wonderfully odd cacti. Celebrate their as the evolutionary wonders that they are!

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]