By Wayne Handlos, Ph.D.

1.2.  3. 4. 5.

               (Photos by Wayne Handlos, unless otherwise noted.)

1. & 2. Typical ‘Mr. Wren’ flower and leaf

3. 'Mr. Wren' with branch of all red flowers  4.  All red sport of ‘Mr. Wren’

5. 'Mr. Wren' and Sport   (Photo: GATW, 1980. Vol. 28, #1, p. 11. - San Diego Geranium Society)


Since their origin about 300 years ago, the zonal Pelargoniums (P. x hortorum - initially hybrids

between P. zonale and P. inquinans) have given rise to new types through a number of mutations.

 Horticulturalists are always alert to different types of flowers, leaves and habit among their garden

plants and these mutations (commonly called sports) are cherished and propagated for their novelty

value. Through the years these novelties have given rise to new classes of plants – which are

recognized by gardeners and end up in flower show schedules.

In the flowers of zonal Pelargoniums, these novelty types include double and rosebud flowers, fringed

or carnation-type flowers, cactus flowers, tulip flowers, bird’s egg, phlox eyed, painted lady, New Life,

Mr. Wren, formosum, stellar and green flowers. Mutations affecting the leaves have given rise to the

variegated or fancy leaved Pelargonium, while mutations affecting stature led to the miniature and

dwarf categories of plants.

Over the next months, I will examine each of these flower categories in turn.

‘Mr. Wren’

In the zonal geranium world, ‘Mr. Wren’ has been in a category of its own. In the bright red, single flower

of this cultivar each petal is bordered with white brush-marks and it is truly an eye-catcher. The plant

grows tall and branches irregularly. It blooms at sporadic intervals so it is a challenging plant for exhibition.

In recent years, an improved version has been introduced by the British firm of Thompson and Morgan. It

is touted to be virus-free, shorter and more compact in growth habit. (See Compost 2.)

‘Mr. Wren’ has been part of the commercial world since the 1950’s. It was introduced by a Mr. Conn who is reputed to have

got it from a Mr. Wren in Oceanside/Carlsbad, California. (Problematic claims associated with ‘Mr. Wren’: It was named for

Christopher Wren, the great English architect. It was found in Connecticut – abbreviated as Conn. It has been called ‘King Tut’.

And Peggy Schultz, well-known American garden writer, claims she grew it from seed.)

Microscopic views of the petal epidermis of ‘Mr. Wren’      (photos by Wayne Handlos)

If you have grown ‘Mr. Wren’, you may have found that it occasionally produces clusters of all red flowers - the white margin is

totally absent. This phenomenon gives you a clue about the nature of this plant. ‘Mr. Wren’ is a periclinal chimera. (See for more information about chimeras.) In other words, it consists of cells with two different genetic

compositions. One group of cells carry the information to produce flowers with white brush-marks on the petals. But another

group of cells do not carry this information and produce all red flowers instead. Tilney-Bassett and Sylvia Plaschil have both

investigated ‘Mr. Wren’ with similar results. In the stem apex of pelargoniums, there are three cell layers – designated as L I,

L II and L III. Cells from L I become the outer layer of cells of the plant, i.e. the epidermis and the genetic expression of petal

color of the plant is shown only by the epidermal cells. The next layer of cells (L II) gives rise to the cortex of the stem, the

mesophyll (green tissue) of the leaf, the inner cell of the petals and the reproductive structures of the flower (in particular the

 anthers and pollen). Cells from L III produce the innermost cells of the plant body. It is believed that the cells derived from L I,

the epidermis, carries the red/white pattern information for the flowers of ‘Mr. Wren’. The other layers of cells, L II and L III,

lack this information and plants which develop from these layers produce flowers with all red petals. Tilney-Bassett designates

this plant as RWGG corresponding to the genetic composition of the three cell layers, L I, L II, L III respectively. When a plant

produces a shoot with all red flowers, it is thought that the cells of L I are replaced by cells of the next inner layer, L II, so the

composition of the plant is now designated as GGG.

‘Mr. Wren’ can produce seed if self-pollinated and if these seeds are grown out the flowers are either red or salmon colored in

the ratio of 3:1. There are no white edges. The reproductive cells of the flower are derived from cells of the L II layer which lacks

the genetic information to produce white petal margins. The red/salmon color segregation indicates that the plant is heterozygous

 for the red color.

Neither Tilney-Bassett1 nor Plaschil2 were able to establish a plant from the cells of L I so its further characteristics could not be

determined nor could it be used for breeding. In Tilney-Bassett’s lab, he never found an all-white flower on ‘Mr. Wren’ but one

was illustrated in 1980 in GATW without comment.

          1 Tilney-Bassett, R. 2008. Variegated zonal Pelargoniums. Serendipity Press, Darlington, U.K. 252 pp.

               2 Plaschil, S. 1997. Vergleichende Untersuchungen zur histogenetisch bedingten Sternmusterbildung in der

                 Petalenfärbung bei Camellia L., Myosotis L., Pelargonium L’HERIT., Phlox L.,Rhododendron L., Saintpaulia H. Wendl.,

                 Verbena L. Dissertation, Humboldt Universität, Berlin. 122 pp.


Plaschil has studied this flower pattern in other plants – Camellia, Phlox, Rhododendron, Saintpaulia and

Verbena – with results similar to Pelargonium ‘Mr. Wren’. This pattern is referred to as "pinwheel" or

"pinwhirl" by her.

6.     7.        8.]       9.

6. ‘Natalie’     7. ‘Frou Frou’          8. ‘Pink Ice’             9. ‘Picotee Kliener Liebling’

  10.     11.        12.

10. Zelda’s Camellia      11. Phlox ‘Candy Stripe    12.Verbena ‘Aphrodite’

13.13. ‘Humako Tineke’

Sources of images.




9.     10.-12.  no image source available


   ^This website ( link 13.) has amazing information about African Violet chimeras.


While ‘Mr. Wren’ appeared to be unique in its floral pattern, the same condition has been seen in the other groups

mentioned above. A search of the internet turns up four other cultivars of zonal Pelargonium with similar patterning

 – ‘Natalie’ (salmon and white, semidouble; a sport of ‘Deacon Mandarin’), ‘Frou Frou’ (a double, pink and white,

standard zonal from Vernon Nursery), ‘Pink Ice’ (another double with pink and white flowers but a miniature) and

‘Picotee Petit Pierre’ also known as ‘Picotee Kleiner Liebling’, also a miniature.

So, ‘Mr. Wren’ remains an intriguing and somewhat mysterious plant (but not quite as unique as once thought).

© 2015, Central Coast Geranium Society (CCGS )