Friday, November 7, 2014

Hybrids in Horticulture

Horticulture abounds with hybrids; some were intentional crosses and some occurred when nature got frisky and did it herself. The origin of "hybrid" is from Latin ibrida, then hybrida, which originally meant the offspring of a tame sow and a wild boar, or a child of a freeman and a slave etc.

Sarracenia x wrigleyana 'Scarlet Belle'

Sarracenia x wrigleyana 'Scarlet Belle'

Darlingtonia californica

Our state-employed plant inspector loves to muse about our carnivorous plants, for he also grows some as a hobby, although he haughtily proclaims that he's into the species only and not the hybrids. So he's not interested in our 'Scarlet Belle' cultivar, even though each clump can produce up to 100 pitchers. But Mr. Inspector, don't you know that 'Scarlet Belle' is a selection of S. x wrigleyana, which is itself a naturally occurring hybrid of S. psittacina and S. leucophylla? The genus Sarracenia was named after Michel Sarrazin (1659-1734) a Canadian surgeon, scientist and naturalist. He was born in France, but plied his craft in New France, the huge area east of the Rockies, from Newfoundland down to the Gulf of Mexico. Dr. Sarrazin probably collected S. purpurea, which is now the provincial flower of Newfoundland. I've never seen any Sarracenia species in the wild, but I have discovered the closely related Darlingtonia californica on a few occasions. My wife doesn't like any of them – they give her the creeps, as the pitchers look like cobra-heads.

Acer shirasawanum 'Sensu'

Acer shirasawanum 'Sensu'

I think that if you sow seed from any Acer shirasawanum that is growing in a garden setting with palmatums, you are liable to produce a cross of the two species. The offspring might be pure shirasawanum, or else it is a hybrid, and of course you cannot achieve a pure palmatum from the cross. There are a number of distinctions that differentiate palmatum from shirasawanum, but the most obvious is that shirasawanum produces seeds that rise above the foliage, whereas palmatum seeds dangle beneath. So Acer shirasawanum 'Shira Red' has upright seeds, but Acer shirasawanum 'Red Dawn' has its seeds beneath the foliage. Nice name – 'Red Dawn' – but it should not be classified as a shirasawanum. I suppose you can have various percentages of the hybridizing species in each seedling, or at least various traits of one species versus the other. Acer shirasawanum 'Sensu' arose as a seedling from Acer shirasawanum 'Palmatifolium', which is itself a probable hybrid. So where does that leave us? Well, I don't know since my knowledge of botany is very limited. I probably didn't have the brains to be a botanist, but I imagine that a career in botany would be endlessly fascinating.

Acer x conspicuum 'Phoenix'

Acer x conspicuum 'Silver Vein'

The stripe-bark maple species can easily hybridize. The cross of Acer davidii and Acer pensylvanicum is aptly named x conspicuum, and some selections from that cross can be remarkable. 'Phoenix' features red bark with white striations in winter. In summer, however, it is a plain-Jane, but it's always worth the wait to see how brightly red it will become. In deep shade the bark is not so colorful, but the foliage is more happy, at least in Oregon. A. c. 'Silver Vein' is also a beauty with a lot of silver to the trunk. The x conspicuum (yes, two u's) hybrid is a fast-growing tree which will eventually form a broad crown.

Acer x coriaceum

Acer x coriaceum is a small deciduous tree with a neat canopy, and resulted from a cross of Acer monspessulanum with Acer opalus ssp. obtusatum.* Tiny leaves are glossy-green, then turn to butter-yellow in fall.

*Those parents are according to Hillier in Manual of Trees and Shrubs; but Beaulieu in An Illustrated Guide to Maples lists the parents as A. pseudoplatanus x A. monspessulanum. In any case, coriaceum was named over 100 years ago, and was derived from Latin coriaceus meaning “leathery” due to the texture of the leaves.

Acer x dieckii

Acer x dieckii was named for Georg Dieck (1847-1925), a nurseryman near Berlin. It will grow larger than Acer coriaceum because its parents are A. platanoides and A. cappadocicum ssp. lobelii. Both x dieckii and x coriaceum are noted for impressive yellow flowers in spring, and old specimens seem to show off with thousands of blossoms, a virtual yellow cloud.

Acer macrophyllum

Acer circinatum

Acer glabrum ssp. douglasii

The three Acer species native to Oregon – A. macrophyllum, A. circinatum and A. glabrum ssp. douglasii – can be found in close proximity in the Columbia River Gorge. I can show you a place where all three species touch each other, yet they never hybridize. Glabrum is in the section Glabra, macrophyllum is in the section Lithocarpa and circinatum is in the section Palmata. It's odd that Oregon is considered the "Maple Capital of the World" by growers and collectors of Acer, yet we only have three native species.

Rhododendron x 'Blewbury'

Rhododendron x 'Blewbury'

I have more Rhododendron species plants in my collection than I do of hybrids, but some of the hybrids I like very much. Rhododendron x 'Blewbury' is R. anwheiense crossed with R. roxieanum var. roxieanum, and its flowers are bell-shaped and white with reddish purple spots. It is called a "medium-sized evergreen shrub" by the Royal Horticultural Society, but my 15-year-old specimen is only 4' tall by 4' wide. 'Blewbury' was produced by Waterer at Windsor, England in 1969, and it received the RHS Award of Garden Merit.

Rhododendron x 'Ever Red'

Rhododendron x 'Ever Red'

Rhododendron x 'Peter Cox'

Rhododendron x 'Peter Cox'

Rhododendron x 'Ever Red' displays lush brown-red evergreen foliage with deep red flowers. I first saw it (and bought a start) from the Rhododendron Species Garden in Washington state. I was told that it was a Glendoick hybrid from Perth, Scotland, but I don't know its parentage. Kenneth Cox is the third generation owner of Glendoick, but I've never been there myself. Another Rhododendron hybrid that I'm fond of is x 'Peter Cox', who is Kenneth's father. Its parents are R. leucaspis and R. carolinianum, the latter now considered R. minus (Carolinianum Group). I know that everyone thinks he or she is right when it comes to Rhododendron classification, even though they never agree. I stay out of the fray as I don't know enough to get in it.

Rhododendron x 'Taurus'

Rhododendron x 'Taurus' is a superb hybrid created by the late Dr. Frank Mossman of Vancouver, Washington. I grow one in my front yard in full sun, and whenever it's in flower I am reminded of Mossman's generosity when I was first starting my nursery. He had a large number of Japanese maple cultivars, as well as Magnolias and Rhododendrons, and I was allowed to help myself. 'Taurus' was a cross of R. strigillosum with 'Jean Marie de Montague', and I think it is a better garden plant than either of its parents. The rest of the world likes it too, for it received the RHS Award of Garden Merit.

Rhododendron x 'Winsome'

My Rhododendron x 'Winsome' belongs to a Winsome Group, which I think means that there are variations between one 'Winsome' and another. Lord Aberconway of Wales crossed R. griersonianum with R. Hummingbird Group in the 1930's, the latter being R. haematodes ssp. haematodes x R. williamsianum. I don't expect you to remember that, and I myself will have forgotten by Monday. In any case my 'Winsome' is a nice compact (smaller) evergreen shrub with a surreal pink flower. Our bush is planted in shade along our creek, behind the Box Area Greenhouses. When an ex-employee – who professed to hate Rhododendrons – walked through a greenhouse and suddenly stumbled upon the 'Winsome' in full bloom, he exclaimed in shock, "Wow."

Rhododendron x 'Pink Snowflakes'

Rhododendron x 'Seta'

Rhododendron x 'Pink Snowflakes' is a cutie and I only have one plant left. It was so popular that I easily sold the rest when I acted on an urge to make money, as well as to simplify my propagation. Now I regret it. x 'Pink Snowflakes' is a cross of R. racemosum with R. moupinense, both Chinese species of small size. Rhododendron x 'Seta' is another R. moupinense hybrid, but in this case with R. spinuliferum, and it is the first Rhododendron in my garden to flower (in March).

Magnolia x 'Genie'

Most of the Magnolias in commerce today are hybrids. One of my favorites is the new x 'Genie', which I have hyped a lot in the past year. Surprisingly Hillier says that the M. x soulangeana and M. liliiflora cross "has not done well in a number of gardens in the British Isles, the branches dying back."

Magnolia x brooklynensis 'Black Beauty'

I planted a Magnolia x brooklynensis 'Black Beauty' along the road to my house, and when it was only five years old it began to flower. The blossoms are not actually black, but they are a very deep purple, and the white interior seems to intensify the outer darkness all the more. M. x brooklynensis is a cross of M. acuminata and M. liliiflora, and was bred at the Brooklyn Botanic Garden's Research Station by Dr. Lola Koerting. x 'Black Beauty' has a nice upright form due to its acuminata parent, and it is hardy to USDA zone 4.

Magnolia x 'Yellow Bird'

Magnolia x 'Elizabeth'

Magnolia x 'Yellow Bird' also uses M. acuminata, and is then crossed with M. x brooklynensis 'Evamaria'. Blossoms are small but they are numerous and very yellow – not the washed-out cream yellow of M. x 'Elizabeth'. It too was bred at the Brooklyn Botanic Garden and is hardy to USDA zone 4. x 'Yellow Bird' has a catchy name, and it begins to bloom when it is young.

Magnolia x 'Red Baron'

Magnolia x 'Red Baron' was hybridized in Wisconsin by Denis Ledvina, so it should be hardy for all of us. It blooms late when the leaves are present – according to many – but you can see from the photo above at Flora Farm that the foliage hadn't yet developed. I'm sure I have the correct cultivar, as the scions were sent by Mr. Ledvina himself. My tree is a strong grower with a narrow crown, and its parents are M. acuminata x M. 'Big Dude'. 'Red Baron' is more hardy than 'Big Dude' and also the blooms are more red.

Carpinus betulus
Carpinus laxiflora var. fargesii

A naturally occurring hybrid of Carpinus betulus and Carpinus orientalis was introduced by Roy Lancaster in 1972. It is named x schuschaensis, a name that you'll always have to look up to spell correctly, but you can just call it the "Iranian Hornbeam." I don't grow it but it's said to be a small tree with elegant branching. Carpinus betulus for me is rather boring, but I would like to see it crossed with Carpinus fargesii – which is now classified as Carpinus laxiflora var. fargesii.

x Chitalpa tashkentensis

x Chitalpa tashkentensis was a cross of Catalpa bignonioides and Chilopsis linearis, and was bred at the Botanical Garden is Tashkent, Uzbekistan in the 1960's. Both parents belong to the Bignoniaceae – the trumpet vine – family. The Chilopsis parent is unattractive to most, and linearis is known as the "Desert Willow." The hybrid eventually made its way into America, but remained unnamed until the Rancho Santa Ana Botanical Garden christened it as x Chitalpa. I have no photos of the flowers, but an important feature is that they are sterile, so messy seed pods do not develop. It is considered hardy to -10 degrees, USDA zone 6, and is very drought tolerant.

Cornus x 'Celestial'

Cornus x 'Venus'

Cornus florida – the eastern dogwood – was once popular, and many Oregon landscapes contained colorful cultivars. At the time I began my nursery, horticulturists began moaning about floridas catching Dogwood Anthracnose from a pathogen appropriately named Discula destructiva. It would strike in dense shady sites with poor air circulation, causing brown blotches on the leaves and twig dieback and stem cankers. So I steered clear of floridas and focused on growing Cornus kousa cultivars. Meanwhile Dr. Elwin Orton at Rutgers University was crossing floridas with kousas, and these proved resistant to anthracnose. Besides, the trees were fast-growing with nice canopies. The hybrid is known as x rutgersensis, but cultivars are commonly known as the "Stellar Series," with cultivar names such as 'Aurora', 'Celestial', 'Constellation' etc. Another Rutgers hybrid was C. kousa var. chinensis crossed by C. nuttallii 'Goldspot', and that crossed with Cornus kousa. The cultivar name for that mixture is 'Venus'. I have a few of Orton's trees in the Flora Wonder Arboretum, and they're easy to spot in landscapes for their large flower bracts. I have never sought permission to propagate them, and a good thing, for they quickly became a glut on the market.

Sorbus americana

Aronia 'Autumn Magic'

Sorbus commixta

There are a number of intergeneric hybrids listed in The Hillier Manual of Trees and Shrubs (8th Edition) which involve the genus Sorbus. I don't grow any of them, but I would like to see how they look. x Sorbaronia is Sorbus x Aronia, and includes the species alpina, dippelii, fallax, hybrida and sorbifolia, and these variations involve different species of Sorbus and/or Aronia. For example, Sorbaronia alpina is Aronia arbutifolia x Sorbus aria, while Sorbaronia sorbifolia is Aronia melanocarpa x Sorbus americana. Who can remember all of that? Hillier also lists x Sorbocotoneaster which is Sorbus crossed with Cotoneaster. This hybrid was found with the parents in eastern Siberia and "two forms are said to occur, one tends towards the Sorbus parent and the other to the Cotoneaster parent." Another intergeneric hybrid that surprises me is Sorbopyrus where Pyrus communis is crossed by Sorbus aria. I assume that someone could, or already has crossed Sorbus with Crataegus, as we have successfully grafted Sorbus commixta onto Crataegus rootstock.

Probably these Sorbus crosses are done by botany professors with too much time on their hands, and you have to understand that the hybrid may not be better than the parents. Sycoparrotia (Parrotia persica x Sycopsis sinensis) comes to mind as an unnecessary tree.

x 'Harumi'
x 'Saya'

Two very impressive hybrids were achieved by intentional crosses of Homo sapiens var. japanesica with Homo sapiens var. america, as most would agree that the offspring are an improvement over the parents. Isn't nature fun?

1 comment:

  1. Its Lord Aberconwy to be precise. Aber means river mouth in Welsh the language of a people living on the west coast of the British Isles. Conwy is a river in North Wales joing the Irish Sea at the town and castle of Conwy.

    Mike Mc Carthy