This genus exists of swordtails and platies (also called platyfish). The name "Xiphophorus " is a composition of two Greek words, meaning "dagger" and "bearer". Looking at swordtails, you'd expect it to be referred to the sword shaped tail but it actually refers to the gonopodium.
Note: Not all swordtail males do develop a sword and with some platy strains males can develop a very short swordtail. With this being said, the sword (elongated lower finrays of the caudal) seems to be a sexual preferable trait to female swordtails and female platy fish. It's known that swordtails and platy fish are able to interbreed with another. It's also known that female livebearers decide wether a certain male is allowed to mate with her (no matter how often a random male may chase her and even tries to aim his gonopodium in her direction). But if a male swordtail or a male platy with a sword is present, she'll most likely prefer such a male to be her mating partner instead of a male with no sword. Which makes it also more likely that a female platy will choose to mate with a swordtail than with another platy when both species are kept together in one tank. So, in reference to mating selection in general, female of Xiphophorus species prefer swords of male swordtails and platy fish more than the coloration on the male's body.

The name "Platy" is derived from the scientific name of the genus "Platypoecilus" before this species was listed within the genus "Xiphophorus".

Swordtails inhabit waters ranging from Belize, Honduras, Guatemala and mainly Mexico. Platies occur in Mexico, northern Guatemala and Belize. Swordtails do occur in freshwater but also in brackish waters. They can even get used to marine water just like mollies. But just like guppies, swordtails and platy fish were also introduced by man to other waters all over the world. For a lot of swordtail strains do occur in higher situated areas where it can be a lot colder which makes them excellent inhabitants in other colder areas. This tells us as well that we should label swordtails as being subtropical instead of tropical.
There are so many different swordtail and platy species in the wild. The fancy swordtail strains we know are all derived from the Xiphophorus hellerii and the fancy platy strains from the Xiphophorus maculatus and the Xiphophorus variatus. But again, besides these three... there are way more wild species of swordtails and platies.

All swordtail and platy fish species found in other areas on this globe are introduced by man and are therefore feral strains.

Overhere a summary of all wild caught swordtails and wild caught platy fish (which were used for research) and their GPS locations as far as known of course:

Overhere a phylogenetic tree of all known wild Xiphophorus species:

Xiphophorus maculatus & Xiphophorus variatus

The most common varieties of platies which are available through retail are the maculatus platy (Xiphophorus maculatus) and the variatus platy (Xiphophorus variatus). In wild nature these two platy species are naturally wide spread. At the different locations where these platies are found, the wild phenotypes differ a lot in coloration and pattern. Eventhough, this is a fact, but each population found in free nature is one and the same species wether that might be a maculatus population or a variatus population. They're all color morphs of the same kind of platy species. Environmental factors are in play why a different phenotype occurs at a different location.

Already between 1912 and 1934 different such color varieties were imported and bred in the aquarium, so “pulchra” (= the beautiful one), “rubra” (= the red one), “nigra” (= the black one) or “cyanellus” (= the blue one). The fact that these are not independent species, but only color variations, is made clear by the fact that several varieties often occur at the same locality. These color varieties form the basis for the many Platy breeding forms that exist today in the aquarium.

Note: Males of the Xiphophorus species may develop a so-called "pseudo gravid spot". This phenomenon happens mostly with platy species in comparison to swordtail species. Mostly such a pseudo gravid spot will be developed during or after the transition of the anal fin into a gonopodium. It hardly happens before the anal fin's transition. This has got nothing to do with a female turning into a male. For that's a different story.
A gravid spot of a female is the most translucent part of the skin while a pseudo gravid spot is developed in the skin (and absolutely not translucent). But once a pseudo gravid spot is developed, it will never fade nor disappear.

Above: An adult male Xiphophorus evelynae.
Note: Once a pseudo gravid spot has shown on a male's body, it will never disappear.

Sex change:
Platy species "can" be born with both male and female gonads. Which makes it possible that female specimens can change gender. Even when she's been pregnant before. But in that case, the female will keep her gravid spot. And the transformed specimens will be functional males when it comes to reproduction. In general, such a transition will take place after a certain trigger . An example could be an unbalanced male/female ratio within the group or even a lack of hierarchy within the group. But there are more triggers to establish a sex change.
Males however can not change gender for the transition of the anal fin into a gonopodium is irreversible.
 I do have to mention that with platy species we're not dealing with just 2 sex chromosomes (X and Y) like most animals have but with 3 sex chromosomes: W, X and Y. In this case when we're dealing with a female turning into a male, we need females that have the WY or WX combination. WY combination results in functional males and WX combination results in males that won't be able to reproduce. XX females however will always remain female. Males can be of an XY or YY combination.

Note: A sex change does not only happy to Xiphophorus species. It can also happen to a number of other kinds of livebearer species. But not with all kinds. But it happens mostly with Xiphophorus species as best known livebearer family.

If there's a lack of males or even no males within a group but there are fry present, you'll notice that there will be fast developing young males. These males stay small in comparison to an average male's body size. This is to ensure the reproduction and the existence of the species. What's also remarkable with early males is that the majority of their offspring will be male at an average temperature. With late males a majority of female offspring will be the result (and again at an average temperature).

Most fancy platy strains are platies that are of the WY/YY combination.  There's not real evidence of this claim. But it's assumable because of the fact that most color traits in platies are Y-linked. In commercial fancy platy strains, it's desirable that the females look identical in coloration and pattern to the males. Which makes the hypothesis of the WY.YY combination logical. Despite of the fact that this is a hypothesis, it does match the color expectation pattern in the first offspring.
If you'd cross different colored and/or patterned male platies to XX females of one specific platy strain, all male offspring from such a cross will result in male offspring of the XY combination.

Below: The first stages of developing a sword (elongated lower outer fin rays of the caudal fin) in male platies that will develop an actual sword (mind that there are some wild platy species that do develop an actual sword). 

Sexual maturity in both male and female Xiphophorus maculatus:

A sex-linked gene, P, controls the onset of sexual maturity in the platyfish, Xiphophorus maculatus.

The activity of this gene is correlated with the age and size at which the gonadotropic zone of the adenohypophysis differentiates and becomes physiologically active. Immature fish of all genotypes grow at the same rate; however, as adults, males with "early" genotypes are significantly smaller than males of "late" genotypes, since growth rate declines strongly under the influence of androgenic hormone. Five alleles, P(1)... P(5), have been identified from natural populations that under controlled conditions cause gonad maturation between eight and 73 weeks. P(1)P(1) males become mature at eight weeks and 21 mm, P(2)P(2) and P(3)P(3) males between eleven and 13.5 weeks and 25 to 29 mm, and P(4)P(4) males at 25 weeks and 37 mm. Since P(5) is X-linked, no males homozygous for P(5) could be produced. The difference between P(2) and P(3) is largely based upon their interaction with P(5). P(3)P(5) males mature at 17.5 weeks and 33.5 mm and P(2)P(5) males at 28 weeks and 38 mm. The rate of transformation of the unmodified anal fin into a gonopodium, which is under androgenic control, is directly related to the age at initiation of sexual maturity, ranging from 3.2 weeks in P(1)P(1) males to seven weeks in P(2)P( 5) males. These differences may reflect different levels of circulating gonadotropic and androgenic hormones.

In two genotypes of females, initiation of vitellogenesis was closely correlated with size and this critical size was independent of age (e.g., 21 mm for P(1)P(1 )). In a third genotype (P(1)P(5)) the minimum size for vitellogenesis decreased with increasing age, so that females would mature as early as eleven weeks, provided they had attained at least 29 mm, but at 25 weeks even females as small as 23 mm possessed ripe gonads. For P(5)P(5) females, which become mature between 34 and 73 weeks of age, there is no correlation between size and initiation of vitellogenesis. In all four genotypes of females examined, egg number is strongly correlated with size, but the regression of egg number on standard length is distinct for each genotype. Late maturation of P(5)P( 5) females is not offset by an increased number of eggs; for this genotype there is a strong negative correlation between age and number of eggs. Heterozygous fish always mature later than those homozygous for the "earlier" allele. The site of action of the P locus could be the pituitary gland, the hypothalamus or higher centers of the brain where peripheral information is transduced into an appropriate signal required for the activation of the hypothalamus-pituitary-gonadal axis. The P gene could also control the peripheral information.

It seems that not all aquarists know the difference between a maculatus platy and a Variatus platy. Not the coloration, pattern nor the finnage will make the difference in appearance to determine a platy to be a variatus or a maculatus.It's the body shape that's the crucial difference (besides DNA) in both Xiphophorus species. The picture below will show the main difference to a layman.

And it also seems that not all aquarists know the difference between a maculatus platy and a common swordtail. Not the coloration, pattern nor the finnage will make the difference in appearance to determine a specimen to be a platy or a swordtail.

It's the body shape and size that make the crucial differences (besides DNA) in both Xiphophorus species. The picture below will show the main difference to a layman.

Wild platies

Mark at the caudal penducle

There are several fancy maculatus platies available. One that I'd like to mention is the so-called Mickey Mouse platy. This kind of platy has derived its name of the head and ears of the Disney character Mickey Mouse. And more like the shape of those Mickey Mouse caps that children can get at those Disney parks all over the world. Many of us know this kind of platy which comes in several colors. But actually, that mark on the caudal penducle is not a fancy trait but a wild trait.

Below: The Mickey Mouse trait. This trait has been crossed into swordtails as well.

The marking on the caudal penducle of wild maculatus platies does differ per wild strain. The picture above shows 4 different kinds of wild maculatus platies with different caudal penducle markings.

Above: Wild Xiphophorus maculatus male specimen. Texas State University - San Marcos.

Below: A summary of different markings on the caudal penducle.

Xiphophorus variatus La laguna
This wild strain can be found close to the east coast of Mexico (state of Tamaulipas). The habitats has got a wide range from southern Tamaulipas, eastern San Luis Potosi and northern Veracruz. In general they inhabit  slow flowing till still waters.

This species does well at lower temperatures and after an average gestation a female will drop between 5-20 fry in general. Good thing is that also this strain will leave their newborn fry at ease. So, creating a colony without a threat of fry eating is potential. 

Above: A juvenile male which is starting coloring up (photo right).

Below: Adult males.

Despite of the fact that males tend to become very colorful, it will take quite long before a male will have its final colors. But not all males will be that bright colored. For it's mostly the dominant males which will become the best colored specimens within the colony. Females don't have that much color but they're well-speckled for that matter. And some females do tend to have somewhat yellow in their fins.

The ones in my possession are descendants from the wild caughts by McAllister, year 2000.

Xiphophorus variatus Puente escalanar

This beautiful wild species originates from Puente escalanar, Veracruz in Mexico and were first collected back in 2002. What's remarkable is that this species has a couple of phenotypes. But most essential is that both genders show a crescent mark on the caudal penducle.  There are phenotypes that have vertical bars on both sides of the chest and there are specimens that are spotted. The body color ranges from greyish till yellowish-golden.

The crescent they show on the caudal penducle is not always very clear. Some have a yellow crescent.

Xiphophorus meyeri

The Xiphophorus meyeri (named after M.K. Meyer, author of livebearer related articles) belongs to the Northern platies. It's also known as Muzquiz platy and Xiphophorus marmoratus.

This platy species has solely been found in two connected ponds in the town of Muzquiz. It's located in the north of the state of Coahuila in the north of Mexico. The waters they inhabit are heavy vegetated.

The Xiphophorus meyeri is listed as being endangered.

The  species knows two varieties: A dark splotched one (marbled) and a non-splotched brown one. Both occur in the same population. But note that the marbled one is born without the splotches. Those occur while aging.

They tend to grow up between 3,5 - 4,5 cm in size. Keeping them at moderate temperatures is sufficient to keep them well. But these platies are a bit  timid and will hide more than the average platy. So be sure they do have sufficient hiding spots.

Further on to keep them well, it's important that a water change will take place regularly.

Xiphophorus evelynae
A wild strain platy close related to the Xiphophorus variatus is the Xiphophorus evelynae. This strain is also known as Highland platy.
This platy is mainly found in the fast flowing Rio Tecolutla stream close to the village Necaxa in the state of Puebla (Estado Puebla) in the eastern part of Mexico.

This species prefers densely vegetated tanks to hide and sufficient swimming space for they tend to be vividly. Despite of their vividness, they're real friendly fish. In general they're greyish till light brown bodied with some spots on their body. They do show some yellow in their fins.

It's a prolific kind of fish which doesn't seem to chase their fry. Also with this strain I do keep the new offspring with the adult fish. Males will size up to 4 cm and females tend to size up to 6 cm. 

While doing well at lower temperatures ( 15°C - 21°C) makes this a very easy to keep type of fish. A real good contender to keep outdoors during spring and summer.  

Xiphophorus xiphidium

There are four phenotypes of the Xiphophorus xiphidium The so-called "one spot", "two spot" and "crescent" variety. And the variety with a clear caudal penducle.

This Xiphophorus xiphidium is endemic to Rio Santa Engracias at Tamaulipas in Mexico. It's a platy which has got a short bottom sword unlike other platies. It's a vey easy and hardy fish to keep. 
When males age they tend to get a hump on their backs and tend to develop a pseudo gravid spot. Further on they can also develop a couple of vertical bars on both sides of their body. The number and broadness of those stripes differ per individual specimen.  And there are specimens that are clear bodied (so, no stripes) and specimens that are molted. Males size up to 4cm and females up to 5 - 6cm

The one spot strain which I'm keeping came from a generation wild caught fish in 1978. And there was no influence of other platy strains involved.

Above: Art class has paid off... My own drawing with ecoline. The name of this drawing (it's actually also a painting) is: A trio of Xiphophorus xiphidium.

I had some photos as samples to use. 

Below: A juvenile couple. The young male is starting to develop his gonopodium.

As I've already mentioned, there are also two other variations of the Xiphophorus xiphidium called "Two spot platy" and "Crescent platy". The two spot platy is to be found in Rio Purification and the crescent platy in branches of Rio Soto La Marina.

Above: Illustration courtesy of Christiane Musch.

But there are also specimens with no marking on the caudal penducle. All four variations are not sex related. So, both male or female can show those markings on the caudal penducle. But there are also specimens that have a combination of these markings.

Above: As already mentioned before, the phenotypes differ per individual specimen on the body. In the illustration above, the top left specimen has got thin vertical stripes, the top right specimen is a molted variety, the bottom left has got broad stripes and the bottom right specimen has got broad half stripes. But that's not the only difference in phenotype besides the markings on the caudal penducle. They can also differ in body color as you can see in the illustration above. 

The thing is that all phenotypes occur in one and the same colony of Xiphophorus xiphidium. For sure, one can select the desired ones and linebreed them. But I do like the diversity within one colony. And this shows how diverse wild specimens of the same species can be. So, don't think that it must be crosses when multiple phenotypes show up. They're all the same species.

Above:: A small group of crescent platies.

Below: An adult couple of two spot platies.

Xiphophorus milleri
This platy is also called "Catemaco platy".
This species is endemic to the Papaloapan ecoregion (state of Veracruz)  in Mexico. This platy is endemic to shallow tributaries of Lake Catemaco and in shallow mouths (brackish water) of inlets along the shoreline.

Mine are from Margarita Creek, Lake Catemaco, Veracruz, Mexico (Coordinates:18°21'45"N, 95°2'35"W) 2021 JM Artigas.

It's a yellow bronze bodied platy with speckles and mostly a crescent mark at the rear. There's a real difference in body build in comparison to the Xiphophorus maculatus. 
There are also darker bodies males which seem to be also smaller than their bronze colored relatives. Those darker bodied ones came to adulthood too fast (determined on the Y-chromosome). While regular males size up to approx. 4cm, these dark males will size up to approx. 2,5cm. Females however can size up to 5-6cm.

The early males with a darker body, also have a black gonopodium. The male offspring of the small darker males will also phenotypically be darker and small as adults. The male  offspring that is fathered by a normal sized male will also be identical to their father. If a female produces these two kinds of male offspring in one and the same batch, it means that the female has used sperm of at least, two males of both phenotypes.

After a gestation of 3,5 - 4 weeks a number of fry will be born between 10 - 40. The adults will hardly chase their offspring. 

Bigger males and females can show a dark spot on the caudal penducle. Certain males can develop a pseudo gravid spot as a juvenile.

They are best kept at moderate water temperatures of 18°C - 24°C. They do tolerate warmer but that will shorten their lifespan. 

Xiphophorus maculatus, Chuco's place, 2019
A wild Xiphophorus maculatus platy species found in a small lake at Natural Park Biosphere Reserve Pantanos de Centla in Mexico is the following maculatus species as shown below.

The ones I got came from Kees de Jong (friend, author, co-editor at Poecilia Netherlands and a huge wild livebearer enthusiast like me). He caught them back in 2019 when he went on an expedition. He caught them from a small lake called "Chuco's place"(coordinates: N18.37166 - W92.69411), named after a commercial cichlid collector named Chuco. Remarkable is that this small lake is almost completely covered with water lettuce (Pistia stratiotes) and crocodiles are present overthere. In this lake occur as well Pseudoxiphophorus maculatus, Gambusia sp. and Dormitator maculatus.

This wild maculatus platy is also called "Xiphophorus maculatus Tobasco". This is a name that the german wholesaler Glaser gave to this platy. But I prefer to use the original name "Xiphophorus maculatus, Chuco's place 2019". This is also out of respect towards Kees de Jong.

This X.maculatus version is grey bodied. Both genders have a round black spot on both sides of the shoulder. On the caudal penducle is a dark pattern to be seen (which is called a Mickey Mouse pattern or marking). This specific marking is also to be seen in several fancy strains of the Xiphophorus maculatus (the commercial name for such platies is Mickey Mouse platy and comes in several body colors). Btw, there are several kinds of wild platy strains that have a marking (shape may differ) on the caudal penducle.

Despite of the fact that these are wild caughts, they seem pretty hardy. No problems whatsoever keeping them in captivity.

Xiphophorus maculatus Purpur, Belize

The Belize Purpur, also known as Belize purple, was collected by Harry Grier in 2003 at a locality called “Kate´s Lagoon” on the Belize River.  There do occur four colour variants: body red (br), which are the “Belize Purple”, but also spotted dorsal (sd), iridescent blue (blue) and wild type body (+). The abbreviations in brackets indicate the genetic code used internationally by Platy researchers.

This type of platy shows a hump on its back no matter the sex. The same goes for the bluish mark on the caudal penducle. And this maculatus species has got the potential to grow up large. Males do tend to have a more intense coloration in comparison to females.

Xiphophorus maculatus, Rio Verde

Another wild breed of the Xiphophorus maculatus is the "Xiphophorus maculatus, Rio Verde. The Xiphophorus maculatus "Rio Verde" was found near a tributary of the Rio Verde near San Luis Potosi in Mexico. I've collected this species in July 2022 on a short trip to Mexico. Despite of the fact that they were caught in a tributary of the Rio Verde, I do have name them Xiphophorus maculatus, Rio Verde. For I don't think this tributary has a name itself. 

These are not the biggest maculatus platies I've ever seen. But to me it was worthwhile to bring them along to Holland.

Both males and females are a kind of orange-brownish. They've got an orange dorsal. The orange color is also visible in their caudal and dorsal but not completely through. The anal fin is clear (translucent) with a thin black seam on the back of the anal fin.

Thusfar they've bred true. Also very typical in this strain is that they al have a number of vertical black bars on both sides of the body. From what I've noticed is that the number of vertical stripes varies between one and four. So, not all have an equal number of vertical stripes. 

Fancy platies

When it comes to fancy platies, there's a whole variety of them. All fancy platies are derived from the Xiphophorus maculatus and the Xiphophorus variatus. The Xiphophorus maculatus has been firstly introduced in Western Europe in Germany back in 1907. The body shape of both species (X.maculatus & X.variatus) has stayed the same as their wild ancestors. Besides color and pattern, also the finnage can be different with fancy platies. For instance, hi-fin platies like the wagtail female shown below:

Although the Hifin gene is dominant, a fish cannot be homozygous for Hifin (HH), as two doses of the gene are lethal. In order to produce Hifins, a breeder would need to cross a Hifin (Hh) to another Hifin (Hh), yielding 66% Hifins, or a Hifin (Hh) to a normal fin (hh) yielding 50% Hifins. This implies a true-breeding hifin strain is almost impossible. I'm saying deliberately "almost", for there are statements that refer to almost a full batch of Hifins.

Maintaining fancy platies won't take that much effort. They're quite hardy and are omnivores. So, they eat almost everything that's offered to them.

A remark about the scientific name of most breeding forms of platies. Commerciallywise, they're all labeled as being "Xiphophorus maculatus" or "Xiphophorus variatus". But when we're dealing with a breeding form that is a result of Hellerii swordtail x maculatus platy or Helllerii swordtal x Variatus platy, we can't actually label them as being "Xiphophorus maculatus" or "Xiphophorus variatus" anymore. Probably best to label them as "Xiphophorus platy cf.". But in general, we don't give scientifc names to hybrids.

Xiphophorus maculatus Coral red platy

The coral red platy is one of the best red colored platies there is. A good specimen has a deep intense dark red colored body. Some white or blue may be shown in the finnage (on the edges). There's also an old strain from Berlin (Germany) that does even have a blue shine on te body when the light hits the fish.

By the way, the color red is not specifically a fancy trait. For in the wild there are a number of strains that do show a red coloration. But not that intense. The two pictures shown below show two different wild platy strains. Picture 1 shows a pale red wild platy. Photo 2 shows a wild platy with pale red markings.

Xiphophorus maculatus Bumblebee platy

Like the name already suggests, this strain has markings that resemble the pattern of a bumblebee. Most have a golden-bronze body with dark brown till even black patches randomly on their bodies.

A variety of this bumblebee platy is the calico bumblebee platy. They show more spots besides the dark patches and a blue shine. Like the ones in the video and picture shown below.

Xiphophorus maculatus Blackamoor platy

This is a black platy but with translucent finnage. Note that this is not the same as the commercial strain "green lantern". For the green lantern platy has got a very dark blue body with translucent finnage. The blackamoor platies can have black finnage as well but those have a high chance to develop tumorous spots.

Some fin rays can also be black. The Japanese call this "shimi".

Xiphophorus maculatus White 

There's also a white fancy platy strain. I haven't been able to get my hands on white platies with white finnage nor couldn't I breed such a total white specimen.  I only was able to breed white platies with translucent finnage.

'This is not an albino platy! This is a leucistic platy (white body with black eyes)

Size of maculatus platies

Note: Maculatus platies can grow up larger than most people think. 8-10 Cm are not an exception. If the conditions are right, they can grow up massively.

Variatus platy

Also with Variatus platies, there's a whole variety available on the market as a fancy species. The most known variety is the so-called Parrot variatus play. Some are shown in the two pictures below:

Like already been mentioned by me, there are much more color and pattern forms of the Variatus platy. Here are some different phenotypes: