To expand on Bob's explanation a bit.
The majority of wild bearded Iris species in Europe and western Asia (not including the Aril and Regalia groups) have a base chromosome number of 12 (the number of one set of chromosomes). Most of these are diploid (meaning they have a single pair of sets with 24 total). This is the lowest number possible for most of this group. Some (including I. croatica) are tetraploid and have 48). Most of the tetraploids are from warmer/drier climates to the south of Europe and in the Near East. Probably all of these with 12 as the base (haploid) number can be crossed with one another rather easily, but the triploids produced when a diploid is crossed with a tetraploid (with 36 chromosomes) tend to have problems with that odd set when they try to reproduce, so tend to be sterile, or only by chance occasionally produce gametes (ovules and pollen) that have a proper number of chromosomes to pair up with that from other plants.
The tetraploids mostly tend to resembe one another and also I. x germanica, and most have been lumped by some under that name. However, really there are several distinct looking populatoins within this group, and each probably represents a good "real" naturally occuring species. I croatica is one of these wild types, but with a few others such as I. aphylla, it doesn't really fit into the I. germanica concept, even in the broad lumped together sense. These "others", have a very different look about them, and I would eliminate I. croatica from the I. x germanica discussion right here.
The taller/larger species of these tetraploids (hard to say how many are truly distinct and how many are regional variations of the same thing) look like the older Tall Bearded cultivars, and along with Iris pallida and Iris variegata (both diploids) they are the main ancestors of most of the BB and TB Iris cultivars that we now grow. However, some breeders add genes from other wild species to the mix all the time, and some of the classes (but more those smaller than BB and TB) become more mixed every year. A few of the wild tetraploid types most important in early breeding of Tall Bearded Iris include I. cypriana, I. mesopotamica, I. trojana, and I. 'Amas' (= I. amasia, apparently an invalid name, but I. varbossiana seems to be the same species, and the cultivar 'Amas' should probably be I. varbossiana 'Amas').
There is also a group of wild bearded Irises that is different and has a base chromosome number of 8. These are all dwarf species from basically near the north coast of the Mediterranean, and they are the ancestors of most of our "Miniature Dwarf" and "Standard Dwarf" Bearded cultivars. Those that are diploid have 16 chromosomes, and those that are tetraploid have 32 chromosomes. Most cultivated MDB and many SDB Iris have 32 chromosomes and are this ancestry.
Now then, I. x germanica (what is supposed to be the "true" germanica) has 44 chromosomes (give or take one or two). This seems to be [12 + 12 + 12 + 8), and is derived from crossing a 48 chromosome parent with a 32 chromosome parent to get a 40 chromosome Standard Dwarf Bearded type thing with 40 chromosomes (which functions basically as if it is diploid, but it basically has now combined two sets of 8 with two sets of 12 to get a two new (functioning as) haploid sets of 20, yet there are still 4 sets present). There are a few wild reproducing populations of Iris with 40 chromosomes, such as I. marsica, that are of this same make-up. Apparently one of these hybrid "40's" back-crossed with a species with 48 chrosomes (it seems to have happened several times to give us ancient cultivars such as 'Albicans', 'Florentina', assorted "germanicas" and others). It is not clear which parent species were involved (perhaps mostly I. varbossiana types which grow in Turkey and nearby and I. pumila, which grows mostly further west, or perhaps several species, or even perhaps different species for different individual clones) , but it should be possible to figure out by comparing DNA. Anyway, the resulting "44's" seem to be vigorous plants that have been divided and spread around by humans for centuries, particularly in the Mediterranean region, and seem to have been carried to the Americas (at least South America) by the Spanish early on. These 44 chromosome hybrids (functionally they are tetraploids with one mismatched set of chromsomes) can reproduce, but because of that mismatch set of 8 in their makeup, the chromosomes don't behave properly during meiosis, and the fertility seems low when seeds are produced. Even so, most can make some fertile seeds (perhaps by chance sorting, some seeds get the right mix of chromosomes to be viable), and some of these have apparently added to the number of "clones" of the real germanica type hybrids. There are wild populations of these too, mostly along the north side of the Mediterranean, but in theory they are mostly made up of relatively few individuals that have been moved around by humans and then naturalized.
Our Intermediate Bearded class of cultivated bearded Iris mostly have a similar chromosome makeup, and most are produced by crossing Tall Bearded Iris with Standard Dwarf Bearded, since the 44(+/-) chromosome IB Iris also have reduced fertility. Some of the older cultivars are dead ringers for I. x germanica, and cannot be distinguished based on their structure. A few of these that were (or probably were) man-made in relatively recent time include 'Golden Cateract', 'Crimson King', 'Eleanor Roosevelt', 'Southland', and others like them. I. albicans is often not associated with I. x germanica, but it is of this type too, as is I. 'Florentina', as well as all of the sports of these two.
and so on.
Dave Ferguson in New Mexico
To: iris-species@yahoogroups.com
From: eleanore@mts.net
Date: Fri, 28 May 2010 09:49:19 -0500
Subject: Re: [iris-species] I croatica
ï
Thanks for the explanation, Bob.
A few years ago, I got the US version of I germanica from HIPS. It didn't even survive it's first winter here. I croatica has formed a lovely clump in it's 5 yrs here. I got it from Chuck, so maybe he can comment on it.
While I do know my median and dwarf iris very well, I don't know all that much about species iris. I do love them all though.
I'm here to learn. :)
El, near Winnipeg, Manitoba, Canada Z3
AIS Region 16
----- Original Message -----
From: r*@embarqmail.com
Sent: Friday, May 28, 2010 9:36 AM
Subject: Re: [iris-species] I croatica
While it is certaibly true that Iris croatica belongs to a complex of species that have been relegated to Iris germanica, it is not at all bad form to use the name Iris croatica. Iris germanica and its allies have been very poorly studied. Brian along with many western Botanist tend to be lumpers. But the splitters have separated out a number of species. Iris germanica should be a bit of an embarassment for any Iris taxonomist since although it is the type for the genus, and yet it has been very very poorly defined and studied. What is called germanica in the USA is a clone that is practically sterile and triploid. It has been studied enough to believe it is a natural hybrid but the parents have never been figured out. Iris croatica on the other hand blooms later and is quite fertile. It is sad how much we really do not understand. I do not think Brian or anyone else at this time would insist on croatica as only a synonym, even if it is convenient to lump it with germanica.
----- Original Message -----
From: "David Nicholson" <d.avensis@virgin.net>
To: iris-species@yahoogroups.com
Sent: Friday, May 28, 2010 8:03:14 AM GMT -05:00 US/Canada Eastern
Subject: Re: [iris-species] I croatica
Brian Mathew has Iris croatica as a synonym of Iris germanica.
David Nicholson
in Devon, UK. Zone 9b
El Hutchison wrote
<Here's I croatica blooming today. That's one of my raised iris nursery
beds in the background.>
