DRAWING THE LINES
Having decided that a height-based system, with its
admitted faults, is preferable to an ancestry-based one,
we now have to decide how many classes there should
be, and where their height limits should be set.
I believe that the arilbred dwarfs from SDB x aril
breeding (and from other crosses resulting in similar
plants) are sufficiently distinctive to warrant their own
class. They fill a garden niche similar to that of the MDBs
and SDBs, forming cushion-like clumps, whereas the
arilbred medians from SDB x AB breeding (and other
crosses) are more reminiscent of IBs.
Some people have imagined that such thinking will
lead to a whole system of arilbred classes corresponding
to the bearded classes MDB, SDB, IB, MTB, and BB. This
is not the case—those classes each arise from particular
types of breeding that were undertaken in the bearded
irises. The types of breeding used to create arilbreds
are different, and there are no actual analogs to each of
the bearded classes. The proliferation of classes beyond
ABD and ABM would have no theoretical basis and no
practical value.
Although the height limits of the ABD and ABM
classes will need to accommodate irises of many
different types of ancestry, the limits should be set to
give the familiar APTT (SDB x AB) and APT (SDB x aril)
irises natural categories in which to reside. The upper
height limit of the ABM class also needs to be set with
an awareness of the considerable overlap between the
APTT types and arilbreds whose bearded ancestry is
solely from TBs.
When studying the question of height limits, it is
convenient to refer to the different types of crosses by
chromosome configuration, as introduced earlier in this
article. Using A for a set of 10-11 aril chromosomes, P for
a set of 8 pumila chromosomes, and T for a set of 12 TB
chromosomes, we have the following:
diploid aril (AA) x SDB (PPTT), the standard
“arilbred dwarf” cross, gives APT.
halfbred arilbred (AATT) x SDB (PPTT), the
standard “arilbred median” cross, gives APTT.
arilbreds from TB breeding are ATTT
(“quarterbreds”) or AATT (“halfbreds”)
I have looked at the registered height of all arilbreds
in each of these categories, from 1950 through
2016, when height data was available and when the
chromosome configuration could be inferred with
confidence. The data is summarized in the graph
below. (I have binned the raw data into 2-inch bins. For
some reason, hybridizers seem to strongly prefer even
heights to odd heights, creating a sawtooth pattern in
the data that needlessly distracts. The Y axis shows the
percentage of irises of the given type that fall in each
height bin.)
0.50
0.45
0.40
0.35
Arilbed Height Distributions
percentage registered height in inches
0.30
0.25
0.20
0.15
0.10
0.05
34 AIS Bulletin Fall 2018
0.00
4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
AATT, ATTT
APTT
APT
registered height in inches percentage