If a rhododendron has more that the normal number of chromosoms it is called a polyploid.  Most polyploids have either 1 1/2 times the number, called a triploid, or twice the number, called a tetraploid.

John and Sally Perkins have taken an enormous interest in rhododendron polyploids and have had many cultivars analyzed to determine whether they are polyploids.  Here is a partial list of some of the rhododendron polyploids:

Anita Gehnrich Triploid

Anna Rose Whitney Triploid

Antoon Von Welie Tretrploid

atlanticum Tetraploid

austrinum Tetraploid

Beauty of Littleworth Triploid

Broughtonii Triloid

calendulceum Tetraploid

Cotton Candy Triploid

Countess of Derby Tetraploid

Cynthia Triploid

Doreen Gale Tetraploid

El Camino Triploid

Gentle Giant Tetraploid

Gomer Waterer Triploid

Gorgeous George Tetraploid

Grace Seabrook Triploid

Legend Tetraploid

Lem’s Monarch (AKA Pink Wallaper) Tetraploid

Lucky Strike Triploid

Mariness Koster Tetraploid

Phyllis Korn Triploid

Pink Pearl Triploid

Platinum Pearl Triploid

Point Defiance Tetraploid

Phyllis Korn Triploid

Solidarity Triploid

Taurus Triploid

Trudy Webster Tetraploid

Van Triploid

Now you might wonder why polyploids are important for hybridizers.  All you have to do is look at the list above and you will see some very important hybrid rhododendrons.  Most of them are West Coast plants, too tender for most East Coast gardens.  Many of them grow in my garden, but that is not saying much, as I have a very “tender” climate.  So the goal going forward is to see if polyploids can be developed that are hardy in cold climates.  There is one particular hybrid rhododendron that has a standard number of chromosomes, called a diploid, and has shown in the past to produce polyploid hybrids.  It is ‘Jean Marie de Montegue’ which I shorten to ‘Jean Marie’.  If you look at my list of selected seedlings, you will see that I have used it frequently in the past and gotten, I think, some polylpoids in its offspring.