RE: RE: OT: ID a Tree & rebloom news
- Subject: RE: [iris-photos] RE: OT: ID a Tree & rebloom news
- From: "Steven Hill" firstname.lastname@example.org
- Date: Tue, 11 Oct 2005 14:50:31 -0700
- Thread-index: AcXOlyMe5rrip/u+QymE4ZcKLQJk2QAFn9cQ
- Thread-topic: [iris-photos] RE: OT: ID a Tree & rebloom news
Title: Re: [iris-photos] RE: OT: ID a Tree & rebloom news
If this is on behalf of the Bruce and Linda who used to live
in Yakima WA, tell them hello from Steve Hill
You are wonderful. Thank you so
much for all the info!
Have a great day!
There are lots
of good discussions about chromosomes and the results of crossing various
classes and/or species with differing numbers. I think the 'World of
Iris' has some good discussions on the basics. Again I am away from my
resources, so I still can't look up 'Lady Emma', nor cite
Anyway, here is a bit of an "in a nut shell" summary,
that I hope makes sense:
The IB class is mostly derived from crosses
between 40 chromosome species or dwarf cultivars with 48 chromosome TB
species or cultivars, yielding 44 chromosome (give or take one or two) IB
offspring. The old IB cultivars are mostly derived from I. lutescens
crossed with 48 chromosome TB species or cultivars, and certain hybridizers
such as Sass and others made bunches of these. Newer ones tend to be
from TB cultivars crossed with SDB cultivars in search of desirable
character combinations from the two parental classes. Of course they
are all interfertile, so they are crossed with one another too.
Some of the 40 chromosome dwarfs (I know the plural of dwarf
is dwarves, but it sounds wrong for Iris somehow) are hybrids of 32
chromosome dwarf species or cultivars with 48 chromosome TB species or
cultivars, and I. lutescens and other wild 40 chromosome species of bearded
Iris also probably derived originally from 32 chromosome species crossed
with 48 chromosome species. This is overly simplified, as 18 and 24
chromsome species (diploids) may have been involved too - through unreduced
Anyway it sort of works out like this:
(48/2) = 40 This lead to wild species such as I. lutescens and most
cultivated SDB's (which are fertile with species such as I.
As for wild candidates there are a lot, but potential
examples could be as follows. It is likely that the parent species of
the original wild 40 chromosome species were those that occur around or near
the Mediterranean, but things to move around over time. It seems that
more notherly or inland small or smallish 24 and 48 chromosome species such
as I. aphylla, I. croatica, I. junoniana, I. reichenbachii, I. suaveolens,
and their kin. probably weren't involved. Probably not I. variegata
either, though perhaps. Also, these (except for I. variegata, which
was important) mostly weren't involved in early cultivars either, but they
are more and more now:
I. attica (unreduced = 16) + I. pallida
(unreduced = 24) = 40
I. pumila (normally reduced 16) + I.
cypriana (normally reduced 24) = 40
These could be examples of how
wild species such as I. lutescens came to be. They are fertile,
because they have two sets of 8 and two sets of 12, which act as if they are
two sets of 20 (everything is ballanced). They are technically
tetraploids, but functionally they are diploids. This is one way that
chromosome numbers can be instantly and greatly increased through addition
of unlike sets to form new sets.
These tend to be dwarf (mostly SDB),
but not as dwarf as the parent species (mostly MDB) with a base set of 8
chromosomes (the 16 and 32 chromosome species).
When you cross the 40
chromosome plants with 48 chromosome plants, you get an unbalanced set of
one 8 and three 12's (usually - sometimes it doesn't all sort out quite
right and you get 43 or 45, or even occasionally numbers futher away from
44, all the way from 40 to 48, because sometimes things don't sort out quite
as neatly as you might expect). Anyway, these usually end up with 8 +
12 + 12 + 12 = 44, and they are usually intermediate to SDB and TB, yielding
mostly IB plants. The wild "species" I. germanica, I. albicans, I.
florentina, etc. are of this sort of ancestry as well. They tend to be
infertile (they will make some seeds), and due to their most common
ancestries they tend to be early flowering.
The MTB's tend to fall
nearly all into two broad categories. One is the diploids (nearly 100%
of older cultivars) derived mostly from I. variegata and I. pallida
cengialtii, with a bit of other smallish diploid species such as I.
reichenbachii mixed in occasionally. They tend to be late-flowering
with more delicately proportioned stems and flowers than the 44 chromosome
class of (mostly) IB's, and they also tend to have morphological traits
dominated by I. variegata, while the 44 chromosome class mostly look
morphologically most like I. germanica or I. albicans (ignore the flower
The other mostly recent MTB group is very different and is
derived from cultivars of 48 chromosome TB's and BB's (BB's are usually
genetically TB's, but they just don't get as tall), crossed with small
northern 48 chromosome species such as I. aphylla, or cultivars derived from
them. They tend to inherit an earlier bloom time from the small
species and some flower almost as early as the 44 chromosome group, and
often much earlier than most of the diploid MTB's.
All the AIS
categories tend to follow basic genetic groupings, and so MTB's tend to be
mostly 18 or 36 chromosome plants. SDB's tend to be mostly 40
chromosome plants. IB's mostly 44 chromosome plants of recuced
fertility, and TB's tend to be 24 or 48 chromosome plants. There are a
number of dwarves that are 24 or 48 chromosome plants, but they tend to be
mostly wild northern species or species crosses, and not to be too much
involved in hybridization of cultivars (yet).
The MTB's are mostly 24
chromosome plants close to I. variegata, but now there is a second group of
them that are 48 chromosome plants of a different ancestry.
BB's) are mostly 48 chromosome plants of Mediterranean / Near Eastern
species often with I. variegata and/or I. pallida ancestry. But many
old ones (usually smaller) are 24 chromosome plants, closely akin to the MTB
diploids, but usually with as much or more I. pallida than I. variegata in
The problem with the AIS system is that it only uses
measurements as a guide, and plants are inherently variable. So,
sometimes a 44 chromosome plant that would logically be an IB by genetics,
will be a MTB or SDB by measurement. So, they get classed with plants
that are not similar in chromosome make up. The same with 40
chromosome plants. Even though they are genetically most like most
SDB's, they can be larger or smaller than average, and become MDB or IB by
As the years go by, the ancestries get more and
more mixed up, muddled, and genes blended together in new combinations.
However, it is very difficult to get the chromosomes of the base 8
species into plants with base 12 chromosome numbers and visa versa, because
once they are mixed, they don't tend to cross back to either main parental
group very easily. The 40 chromosome intermediates are fertile, but in
effect they are isolated from either parental group by their new chromosome
make-up. When they are crossed with the parental groups in either
direction they tend to yield sterile plants with +/-44 chromosomes or +/-36
The 36 chromosome class doesn't seem to be
well-developed, but they should be mostly MDB plants, and I'm sure there are
a lot of them out there that just haven't been recognized as such yet.
They may even be some of those "problem" parents that don't make fruit
or pollen well, for "unexplained" reasons. These would mostly come
from a cross of (32/2 = 16) + (40/2 = 20) = 36.
The more backcrosses
are tried, the more will be successful, and the more the chromosomes will
get recombined in cultivars eventually. Some day there may be MDB with
32 chromosomes, but with genes from TB's and visa-versa. Also, the
more new species are added to the mix, the more complicated, mixed up, and
interesting the cultivars will become.
And this doesn't even consider
any of the Psammiris, Regalias, Arils, etc., which can and are gradually
being added to the mix too.
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