Some may have already seen the video that I made to cover this topic (and if you haven't, you can here: https://youtu.be/mlWFJOk0Ntw ), but when it comes to covering a subject, I can really only be thorough when writing about it. Plus, a good long read can just be cathartic sometimes, so if you prefer that to film, here we go:
Flytrap-style carnivorous plants come in a number of variations; you have the species that are only *just* technically edging into the category, like Nepenthes inermis, some that use the tactic only part of the time (Triphyophyllum peltatum, Drosera caduca, some now say Triantha occidentalis), and then the proper full-time sticky predators: the majority of the sundews Drosera, their relative Drosophyllum which has a rather unique style of sticky carnivory (rather than the insects just getting stuck to the plant, the droplets transfer to the insects and basically drown them as they fall down the leaf), the rainbow plants Byblis, and then the flat-leaved, often rather succulent and otherwise unassuming looking butterworts, Pinguicula.
The genus name for this group actually references directly how their tactic works. Unlike sundews or rainbow plants, the glandular tentacles that the butterworts have are extremely small, barely extending up off the surface of the leaf and numbering in the thousands on each leaf. Without a magnifying glass or really good eyes, it's hard to see them at all, but if you touch the plant, you'll notice immediately. Each tentacle produces a droplet of dew, but a small droplet, and if you swipe a finger over them it will be coated in this sugar and protein concoction and stretch from the leaf to your finger if you pull back, feeling like a greasy, slimy, or snotty sheen that's just sticky enough to grip whatever it touches. Combine that with their usually small size (most don't get more than a few inches across), the translation of the genus name, "Little Greasy Ones," makes perfect sense. This dew tends to snare primarily small insects like gnats or springtails, as well as pollen floating through the air (some species eat more pollen than anything else). Once grabbed, the leaf will typically either dimple inward or the edges curl around the captured food, and sessile glands within the leaf surface will secrete a fluid filled with digestive enzymes to break down whatever the plant needs in order for it to reabsorb the solution back through those glands.
Most of the butterworts have similar structures overall, with their flat, fleshy leaves spreading out across boggy grounds or, perhaps more often, across rocky surface on cliffside seeps, and thin filamentous roots that do more to keep the plants somewhat anchored to a particular spot than they do much of anything else. A lot of water can be taken up by them in some species (like those in the southeast US that also have thicker roots) though in many the leaves themselves just seem to absorb moisture from the environment, but otherwise they don't absorb nutrients much if at all, and frequently are just holdfasts that are regularly replaced, new ones sprouting between new leaves and stretching out to dig into soil or find cracks in rock. Different groups of species bloom at differing seasonal cues, but they all share the same flower type: one to several glandular pedicels that rise up from the center of the rosettes, each holding up only a single flower. The flowers are often what draw people to these plants, more than the carnivorous traits, hanging upside-down below the calyces with a short nectar tube at the back end of most sometimes in conjunction with a tube that houses the reproductive parts, and the front face of the flower roughly divided into two lobes, an upper with 2 petals that usually form and a lower with 3. Color varies greatly, but all serve the same purpose: attracting animals to pollinate them. Only a few species seem to naturally automatically self-pollinate, and those have the smallest, most inconspicuous blooms overall. Many species also cannot self-pollinate at all, instead needing to cross with a genetically different individual to make seeds (particularly it seems in temperate plants and many Mexican species), but all pollinate the same way:
The anthers of the flower are hidden inside the mouth or corolla tube, just below the calyx and in front of the ovary and just behind a broad, flap-like stigma. Being behind the stigma prevent self-pollination without assistance in most species, even those that can self. An insect or other animal that visits the flower will enter the throat of the bloom, trying to reach the nectar within the spur at the back, and as they do so they brush against the stigma flap, depositing pollen there. Then, as they back out, they lift the flap up and expose the anthers, which covers them in pollen that they will then carry to another flower with some luck. In cultivation, we can imitate this by sticking a toothpick into the bloom behind the stigma and gently dragging it upward, gathering pollen, and then depositing it onto another bloom elsewhere.
Pinguicula are part of the Lentibulariaceae family, grouped alongside two other carnivorous plant genera that, without really diving deep into their evolution, you would never put together (though the structure of the blooms are rather similar in all of them, which hints at their relationships). Their closest relatives are the bladderworts (Utricularia) and corkscrew plants (Genlisea), and it's thought by some that the ancestor of all three may have had a trapping mechanism similar to today's butterworts, but it was modified radically in the other two groups into trap styles found in no other family of carnivores. They likely had an origin on the ancient supercontinent of Gondwana, evidenced by the high diversity of all three genera being situated near to or within Africa or South America, though interestingly the butterworts, despite appearing to be the oldest lineage, neither stayed there nor did they become the most diverse of the groups. Sure, there are a few species found in South America still and one or two in northern Africa, but most butterworts are now found in hotspots within the Mexico/Central American region, and southern Europe. Pinguicula are now found basically radiating out from the mountain backbones that run up from the southern tip of South America (one such truly southern species shown below), through the Caribbean and Mexico, across either coast of North America, and then across temperate regions of Eurasia. Almost none are found in tropical lowlands outside the lands bordering the Caribbean, nor are any found in the Austro-Pacific region.
Ancient as they are, the butterworts have at least diverged into several distinct groups that we generally recognize; out of the approximately 100 or so species three subgenera are currently proposed (and a good overview of that is in the December 2021 CPN issue, an article by Andreas Fleischmann), with 12 extant radiations, which we tend to group into 6 different categories: Northern Temperate species, the crystallina-hirtiflora complex, the southeastern US Warm-Temperate species, the South American temperate group, the Mexican/Caribbean butterworts, and an odd little offset group found in boreal temperate regions with very tiny growth habits and odd flowers that don't really fit with any of the others. The warm-temperate and most Mexican species tend to be the most familiar to people, some of the northern-temperate species frequently encountered in the wild by people in the US, Europe, and northern Asia, and the rest are a smattering of oddballs that are frequently uncommonly seen in cultivation and often rare in the wild.
The northern-temperate species are most species-rich in southern Europe, particularly the mountains of Spain, southern France, and Italy, and are the sole group in the subgenus Pinguicula. They range from fairly standard forms like those of P. vulgaris and grandiflora with flat, 2-6 inch rosettes of leaves that hug rock surfaces or spread across bogs, to strange giants like P. longifolia and vallisneriifolia that live on cliff faces and start out the growing season with short, fairly flat leaves, and then as the season progresses. Many species are rather uncommonly grown outside their native ranges (partly because they have relatively short growing seasons and sometimes just decide to go dormant at the weirdest times, so can sometimes be a struggle to keep long-term if you don't keep up with their cycles; I admit I'm kind of poor at putting them in the fridge at the right time, especially when half the pot goes to sleep and the other half keeps growing).
These species have the standard clearly distinct two-lipped flowers, with two upper and three lower lobes on the lips, and typically have a pretty pronounced corolla tube and moderate-length spurs. Most also are colored in some shade of purple or indigo, fading to lavender or violet. Many will also hybridize with each other, but don't seem to readily self-pollinate. Classification is still uncertain for many of the species, as in some areas two different species can look identical, but where they may overlap in range diverge from each other. In addition to seeds (which usually need a cold stratification to germinate), this group also propagates itself via gemmae, little tiny hibernaculum buds that develop as the plant goes dormant, and are readily detached. These are transported by water or ice to new locations, where they wake up in spring as tiny plantlets.
Most of the temperate species are pretty amenable to the standard peat and sand/perlite growing mix, though may appreciate more alkaline or rocky mixes as well, so long as it stays wet. The biggest tricks though are usually to keep them cool through summer (too much heat can drive them to an early dormancy) and to maintain their winter rests properly.
The next general group are the plants from the Mediterranean region that typically grow year round or as annuals; technically two sister groups, these are the crystallina-hirtiflora complex, a funky set of plants in subgenus Isoloba, comprised of the annual P. lusitanica and then the actual sister complex with the bigger, and quite uncommon species in cultivation. The identity of all but that one tiny annual has been frequently contested, whether they're all subspecies or varieties of one variable species, or if they represent several distinct species.
Most of these species are cliff dwellers and often found right down to the coast of the Mediterranean sea so long as there are freshwater seeps to supply them. They also can be found in boggy wet meadows or marshes in some locations, and though placed in Isoloba (which means "equal lobes") they also sport the two-lipped structure seen in most butterworts. The one outlier is the annual P. lusitanica, which gets nowhere near as big as the sister complex (while they may get 4-6 inches across, this dwarf, which also lives further west and north, rarely gets more than an inch or two across, and self-pollinates to spread). To grow these, generally what's needed is to keep them warm and moist all the time, well-fed, and to try and get seeds for the next generation.
Related to these plants are two other sister groups found only in the Americas, but on different continents: the warm-temperate Southeastern US species, and the Andean/Austral temperate species. The first group is fairly familiar, as they are often encountered in cultivation, and love the exact same boggy, sandy swamp and savannah conditions as other familiar plants like Drosera, Sarracenia, or Dionaea.
This group inhabits the Gulf Coastal Plain, with one species (P. pumila) also extending into the Bahamas. Found in longleaf pine savannahs or along the edges of swamps and creeks, they like it wet, sometimes even underwater, and warm most of the year but with a brief cool period in winter. The Primrose butterwort is the most familiar, being as it propagates readily by sprouting plantlets on the ends of its longer leaves (which can form floating mats on water surfaces), but the other species are equally if not more attractive and range from the critically endangered P. ionantha that is rarely seen even in botanical collections, to the diminutive P. pumila that can sport numerous different flower colors (from shades of white and purple to even a rare yellow), to the often bloody red P. planifolia and the sister species caerulea and lutea, both named after their primary flower colors.
This group grows well in the usual peaty carnivore soils most other CP's are grown in, and propagate well from leaf pullings or even cuttings (or as in P. primuliflora, they'll propagate themselves). The one exception is the usually annual pumila, which only seems to do well from seeds. They also need at least a brief exposure (even just for a few weeks) of temperatures down below 50 degrees Fahrenheit, though preferably not actually freezing, in order to really trigger spring flowering and stave off the collapse that they can sometimes show after a couple years in stable temperatures. This group also tends to self-pollinate well (if being a little touchy about timing; you have to get it right to get seeds), but they don't hybridize as far as has been seen so far.
Down south the relatives of this group are real oddballs, tiny species that often only get between 1-3 inches across and thrive in the high seepages of the Andes, or bogs and wet moss pads as far south as Tierra del Fuego in Chile and Argentina. If they're not experiencing cold, stable conditions year round (the tropical mountain species), then they may be buried under snow for half the year or more. This group is also rarely seen in cultivation partly because they haven't been widely distributed to grow, but also because they can be tricky to keep right. Don't give them the cold that they need in one form or other, they may just crash or even flower themselves to death.
I have experience with only one species in this category, and have found it to be rather easy so long as one rule is followed: every year, for at least 4-5 months, it goes in the fridge and stays there. The seeds need no special treatments to sprout and these species can often be self-pollinated, and they don't form winter hibernacula or different leaves, so you just have to be content with exposing what looks like delicate soft tissue to cold or even snow to make them happy. They don't slow down, they just halt growth in winter or in cooler months.
The fifth group is a weird set of plants that seems to mix together traits of the others; P. alpina is in a clade of its own related to Mexican butterworts more than anything else it seems, but is found from above the Arctic Circle to the Himalayas and goes dormant just as the other cold-temperate species do. It has white flowers with a bright yellow patch at the base of a huge lobe on the lower lip, and tends to like locations with a mix of peaty, organic soils and alkaline rocks. Then there is the "dwarf temperates," plants that often don't exceed an inch in diameter in their rosettes, have really hairy flower stalks, and either live in cool locations where they act as annuals or short-lived perennials, or live deep in moss pads in bogs in high latitudes and go dormant in winter. P. spathulata and ramosa are east-Asian endemics, one from Siberia and the other Japan, while algida is a European specialist and villosa circumboreal, but a truly Arctic specialist that thrives in freezing mossy permafrost regions. Most are touchy to cultivate if cultivated at all, and require freezing conditions to work.
The last group is the one that is probably gaining the most attention: the Mexican and Central-American species. With incredibly variable coloration in their flowers and diversity in flower and leaf form, these are also split into several groups within themselves: the northern Andean endemic P. elongata all on its own that dies to dormant buds during dry seasons and likes fairly cold, rocky conditions to grow in, the Caribbean annual or tropical perennial group of which few are grown and many endemic to Cuba (including the unique epiphytic species casabitoana and lignicola that only live on pine trees, and produce seeds that actually being sprouting and growing before the pods ripen) and their almost-sister group the dwarf annuals from Mexico (crenatiloba, pygmaea, lilacina and their relatives), and then the true Mexican radiation with such grand species as gigantea, laueana, mesophytica, macrophylla, heterophylla, gypsicola, and so many more.
Some species in the Mexican radiation are homophyllous, like gigantea and emarginata, meaning they grow in places that are constantly moist like the high cloud forests or more permanently wet tropical regions further south in Central America. These often like to grow in mossy or peaty soils with some rocky matter mixed in, and can do well alongside other carnivores (though generally don't like to be as soaking wet, as they often do grow on cliff faces or moss pads on rocks or trees in the wild rather than on deep soils on the ground).
And then there are the heterophyllous species, a group that has likely gained the most popularity out of all the butterworts due to their sheer variety and also tendency to tolerate being forgotten about much like succulents (particularly in winter when they like it DRY), and can be grown in things as bare as a literal rock in a dish, or pure perlite or sand in a pot (they in fact prefer this over peat or sphagnum, as too much organic material and moisture can trigger them to rot). They often live in the lowland semi-desert regions or in the mountain ranges of Mexico on cliff faces and sand deposits that are moist for part of the year, but then dry out for much of winter even though temperatures don't change much (a bit colder, but almost never freezing). A few of these species possess a habit similar to that of the northern-temperate plants, in that when the winter season comes around they die back to tight, dormant buds that hide underground (these include medusina, heterophylla, acuminata, parvifolia, and a few others).
The others have modified this changed-growth trait however, never actually going dormant in winter but instead simply changing the structure of their leaves to conserve moisture while still being able to photosynthesize and sometimes even flower in the dry season. In summer the leaves are broad, or slender like moctezumae, and carnivorous, but in winter they shrink and multiply, turning into shingle-like hairy overlapping pads or thick, succulent clusters that no longer capture insects, but instead prevent the plant from drying out until summer rains return.
Perhaps the most exciting thing about this group though, at least for horticulturalists, is that they can almost all cross with each other. The two big sections Agnata and Orcheosanthus that contain the majority of the Mexican radiation are sister, and relatively recently derived, so despite containing plants that look completely dissimilar to each other, most can hybridize to create an immense variety of hybrids. Some of these hybrids are sterile, others can only cross with the original parents, but there are a select few that can even make complex crosses, mixing the traits of 3 or more species to create wild looking leaves and incredible flowers.
This diversity in both species and hybrids has resulted in dozens of fairly easy to grow, widely accessible plants and many named cultivars as well (some famous ones include 'Aphrodite', 'Libelulita', 'Sethos', and 'Red Starfish'), and there's a plant that fits just about any sort of growing condition among them. Want something you can forget on the windowsill all winter? Or something that will fit on a decorative rock or hanging planted wall? Or something to mix with other carnivorous plants? The Mexican butterworts probably have it.
Among any of these species though when growing them, it's important to remember where they come from, especially as many of these places are threatened. While species like P. vulgaris or alpina may be found across several continents and have populations that number in the tens of thousands, many of these species are endemic to single mountain peaks, canyons, or small ranges with specialized soils in the wild, places that are easily damaged by human activity or changing climate. We're lucky that they don't really lend themselves to poaching efforts, as they are not the kind of plant that survives well set haphazardly in a box and shipped halfway around the world without special care, but any other activity in their natural ranges can spell threat quite quickly. If you grow anything in this genus (or any plant really), take the time to look up where it comes from, see what activities are ongoing within or near their habitat ranges, and then perhaps find out if there are organizations in those regions or with a broader hand overall (like the International Carnivorous Plant Society itself which assists the efforts of groups worldwide) that you can support so that they can in turn work to protect these spaces, and keep the species alive in the wild for generations to come.
After all, it's one thing to see one clone of one species in a pot in your room, but something else to see thousands of unique individuals spread across a dripping cliff face in a cloud forest in the wild.