Typical ‘Mr. Wren’ flower and leaf
THE OTHER ZONAL PELARGONIUMS – 1. MR. WREN
By Wayne Handlos, Ph.D.
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 zonalPelargoniums (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.
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 geraniumsonline.com 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’6. 7. 8.
(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 geraniumsonline.com 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
nstead. 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 epider-
mal 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-Bassett nor Plaschil 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.
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.
Tilney-Bassett, R. 2008.Variegated zonal Pelargoniums. Serendipity Press, Darlington, U.K. 252 pp. GATW, 1980. Vol. 28, #1, p. 11.
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"
9. ‘Natalie’ 10. ‘Frou Frou’ 11. ‘Pink Ice’ 12. ‘Picotee Kliener Liebling’ 13. Zelda’s Camellia
14. Phlox ‘Candy Stripe 15.Verbena ‘Aphrodite’ 16. 'Humako Tineke'
Sources of images.
9. http://pelargonium-club.com/ 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 zonalPelargonium 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).