Rhododendron viriosum hybrids

flowers of Rhododendron 'Festive Bells'
Rhododendron ‘Festive Bells’

Rhododendron ‘Festive Bells’ is currently flowering in my shade house, so this seems like a good time for a quick post on Rhododendron viriosum hybrids.

R. viriosum is a vireya, a tropical rhododendron, and is one of only two Rhododendron species native to Australia. It has red, bell shaped flowers and is noted for its phenotypic dominance and the vigor that it imparts to hybrids. Hybrids with R. viriosum as a parent almost invariably have bell shaped flowers in some shade of red, and they are usually strong growers. Appropriately, the species name virosum is derived from the same root as the English word “virile”. The species is difficult to locate in the United States, but I am currently growing two first-generation hybrids and have previously grown a third.

Rhododendron ‘Festive Bells’, shown above, is my favorite of the three. My plant, purchased a year ago, is currently blooming for the first time, and the flowers are absolutely amazing. They are some of the best flowers that I have ever seen on a rhododendron, and perhaps on any plant. The color is a pure, intense fire engine red and the flowers have an incredible waxy texture that makes them look as though they are made of plastic. Like many vireyas, R. ‘Festive Bells’ is somewhat lanky with long internodes, but flowers are nicely in-proportion with the plant size. R. ‘Festive Bells’ has R. viriosum as the seed parent, but the pollen parent is unknown.

Flowers of Bovees V97
Rhododendron viriosum x christianae (Bovees V97)

Bovees V97 is an unregistered clone of R. viriosum x R. christianae bred by E. White Smith, former owner the Bovees Nursery in Portland, Oregon. Bovees was for many years the preeminent source of vireya plants in the United States. It closed a few years ago, so I was happy to find this hybrid still offered for sale by Pacific Island Nursery in Hawaii. Genes from R. christianae have imparted orange tones and a more horizontal stance to the flowers, but the plant still has the vigor expected of an R. viriosum hybrid.

flowers of Rhododendron 'Little Maria'
Rhododendron ‘Little Maria’

Rhododendron ‘Little Maria’ was a beautiful little plant that grew in my collection for about five years. The cross is R. viriosum x (viriosum x gracilentum). R. gracilentum is a miniature, cool-growing species from the mountains of New Guinea at altitudes of 2000-2745 m above sea level [1]. Despite the double dose of R. viriosum in the ancestry of R. ‘Little Maria’, R. gracilentum is dominant for plant size. A large specimen of ‘Little Maria’ can fit in a 4″ pot, and both leaves and flowers are about half the size of those of R. ‘Festive Bells’ or V97. Unfortunately, R. gracilentum also seems to be dominant for heat tolerance (or lack thereof). Plants purchased from Bovees died very quickly, but I had better luck with cuttings that I rooted in North Carolina. Anecdotally, I have noticed similar results with other vireyas. When vireya plants in my collection die, it often seems to be because the root system has failed catastrophically in the heat. For some reason, roots that have grown in North Carolina seem tougher–perhaps they have different fungal symbiotes or are better adapted to my potting mix.

Eventually, all of my Rhododendron ‘Little Maria’ cuttings died in the summer heat, and I have been unable to replace them. I am hopeful that V97 will do better in our climate, because R. christianae is from more moderate altitudes of 600-1525 m [1]. Since the other parent of ‘Festive Bells’ is unknown, I will just have to hope for the best, but I have already rooted a cutting as insurance.

Reference

1. Argent, G. (2015) Rhododendrons of subgenus Vireya, 2nd edition. Royal Botanic Garden, Edinburgh.

A modern vireya hybrid

Photo of a vireya rhododendron hybrid
Rhododendron praetervisum x ‘Doctor Hermann Sleumer’

As a complement to Rhododendron ‘Princess Alexandra’, the Victorian vireya that I wrote about in June, here is a more recent vireya hybrid. This plant is Rhododendron praetervisum x ‘Doctor Hermann Sleumer’, so its parentage is R. praetervisum x (konori var phaeopeplum x zoelleri). R. zoelleri has been known since the 1890s, but the type specimen of R. konori var. phaeopeplum was collected in 1939, and the type of R. praetervisum in 1965 [1]. The cross was made by Richard Currie in his New Zealand garden, presumably in the late 1970s or 1980s. One plant of this cross was registered as Rhododendron ‘Cheeky’ but I am not certain if my plant is a division of that cultivar or a sibling.

I previously grew a plant of R. praetervisum, but it never thrived, flowered infrequently, and died after about five years. I’m hopeful that this plant will exhibit hybrid vigor and, perhaps, inherit heat tolerance from R. zoelleri (native altitude range sea level-2000 m [1]). I purchased it in April, and it grew well in my shade house during the summer and has already flowered twice.

Incidentally, Hermann Sleumer was a botanist at the Rijksherbarium in Leiden who described hundreds of new vireya Rhododendron species in the 1950s and 60s, making him one of the most important names in the modern era of vireya cultivation. Both R. praetervisum and R. konori var phaeopeplum (as R. phaeopeplum) were described by Dr Sleumer.

Reference

1. Argent, G. (2015) Rhododendrons of subgenus Vireya, 2nd edition. Royal Botanic Garden, Edinburgh.

Juanulloa mexicana

Juanulloa1

You really can’t go wrong with a hummingbird-pollinated plant. The little birds are attracted to bright colors–primarily red, but also orange, yellow, and magenta–and flowers adapted to hummingbird pollination generally have interesting tubular or bell-like shapes. The only downsides to the hummingbird pollination syndrome are that the flowers usually lack fragrance, and the plants are often not heat-tolerant; hummingbird-pollinated plants are often native to tropical cloud forests where hummingbirds are most diverse and flying insects relatively rare.

Juanulloa mexicana (syn. J. aurantiaca) is a semi-epiphytic shrub that has all the good qualities of a hummingbird-pollinated plant but also exhibits considerable heat and drought tolerance. The plant itself is rather messy–or “interesting” if we want to be charitable. It has long, poorly branched stems that presumably ramble through the branches of host plants or over rocks in its native habitat. The leaves are widely spaced, and adventitious roots can emerge from almost anywhere along the stems. The roots adhere tightly to any surface they come in contact with (greenhouse benches, other pots, the gravel floor of the greenhouse, etc), and once they become large and woody, they can sprout their own leafy stems. When the plant is grown in a pot, roots will creep over the edge and emerge from drainage holes. The thin leaves are subject to infestations of mealybugs and spider mites, and they drop in the autumn, leaving the plant a leafless tangle of stems and roots for much of the winter.

But when it blooms, I forget how inelegant the plant is. The tubular flowers, which grow on short inflorescences, generally near the end of a stem, are dark orange and nestle in a slightly lighter orange calyx. I generally see flowers during the summer, but the plant can also bloom in winter while leafless. My plant seems to be self-sterile; despite numerous visits from hummingbirds and several attempts at hand pollination, I have never obtained seed.

Fortunately, however, J. mexicana is very easy to propagate from stem or root cuttings. I have used moist sphagnum moss and commercial potting mix with equal success, and I suspect that cuttings would grow just fine in damp paper towels or gravel. Stem cuttings will flower more quickly, but root cuttings might give you a more interesting specimen. One of my plants, grown from a piece of root that invaded a neighboring pot, has produced an above-ground tuber which is currently about the size of a plum or very large hen’s egg. Lignotubers are not uncommon in epiphytic shrubs (e.g. epiphytic Ericaceae), and several species of the related genus Markea produce tubers that are often hollow and inhabited by ants. However, I have been unable to find any literature describing tuber growth in Juanulloa. I am unsure if this is normal (i.e. a lignotuber) or abnormal growth (i.e. a burl or something similar). If anyone has any insight, please let me know. I’d be particularly interested to know whether seedlings produce a similar tuber.

Juanulloa2
Tuber at the base of a Juanulloa mexicana plant grown from a small root cutting. Note the new leafy stem sprouting from the old root at lower right.
Juanulloa3
Another view of the tuber

Rhododendron ‘Princess Alexandra’

Rhodo_Princess-Alexandra1

Rhododendron ‘Princess Alexandra’ is a vireya (tropical rhododendron) cultivar, the result of a backcross between the very first vireya hybrid, Rhododendron ‘Princess Royal’ (R. jasminiflorum x R. javanicum), and its parent R. jasminiflorum. It was registered by the famous nursery of J. Veitch & Sons in 1865, from which we can deduce that it was named in honor of Princess Alexandra of Denmark who had married Prince Albert Edward, the future King Edward VII, two years earlier.

Some plants remain consistently popular, while others go in and out of fashion. Vireyas definitely fall in the latter category. R. jasminiflorum flowered in England for the first time in 1849, and over the next fifty years or so, several hundred vireya hybrids were registered, mostly by the Veitch nurseries. Along with orchids and other tropical plants, vireyas graced the conservatories of the Victorian upper class, but their popularity was eventually eclipsed by hardier Rhododendron species which didn’t need an expensive heated greenhouse. It wasn’t until the second half of the twentieth century that an influx of newly discovered species made vireyas and their hybridization popular again. This second wave of cultivation occurred in places where vireyas could be grown outside–New Zealand, Australia, coastal California, Hawaii–and hybridizers focused on species from the mountains of Malesia (the biogeographic region encompassing Peninsular Malaysia, the Malay Archipelago, and New Guinea) that thrived in cool, but not freezing, weather.

In the the years between the first and second periods of vireya popularity, two world wars and a great depression wiped out many of the old collections of tropical plants, and fewer than ten of the Victorian hybrids survive today. I find it amazing that the R. ‘Princess Alexandra’ in my greenhouse is essentially the same plant that grew in the Veitch nurseries. It has been propagated by cuttings and traded among enthusiasts for more than 150 years.

I love to grow vireyas, but unfortunately most vireyas don’t love North Carolina. Although vireyas come from the tropics, most species grow at high altitude, up to and even above the tree line. The montane species–and hybrids dominated by those species–are weakened by our long, hot summers and tend to die suddenly after a few years. I have the best long-term success with the relatively few species that grow naturally a lower altitudes, and it is exactly those species, plants like R. jasminiflorum and R. javanicum, that are the parents of the Veitch hybrids. I’d love to grow more of the old survivors, if only I could find them.

So, if anyone knows where I can obtain cuttings of Rhododendron ‘Ne Plus Ultra’ or R. ‘Triumphans’ in the United States, please let me know.

Rhodo_Princess-Alexandra2

Six on Saturday #57 (June 20, 2020)

Is it Saturday again?  Here are six plants that are currently flowering.

1. Amorpha canescens (leadplant)

Amorpha-canescens

This is a plant that rewards close inspection.  Its purple flowers with golden yellow stamens are gorgeous, but tiny.  A. canescens is native to the central United States, from Minnesota and North Dakota to Texas.  I grow it a sunny, dry location near our rosemary bush.

2. Canna ‘Lucifer’

Canna-Lucifer

The somewhat dull orange-red flowers of ‘Lucifer’ can’t hold a candle to Canna ‘Flaming Kabobs’, but ‘Lucifer is probably much better suited to small gardens.  It is a miniature, standing only 3 feet high with inflorescence (90-100 cm), less than half the height of ‘Flaming Kabobs’.  I am growing it in somewhat poor, dry soil, but it has proven to be a tough little plant and has slowly spread into a clump about four feet wide.

3.  Habranthus tubispathus var. texensis (Texas copperlily)

Habranthus -texensis

This is a rather nice weed.  Seed must have drifted from some potted bulbs, and now a little Habranthus is blooming right at the edge of our driveway.  H. tubispathus has a disjunct range in southern South America, Mexico, the Caribbean, and the gulf coast of the United States.  It seems likely that it was originally native to Argentina, Uruguay, and Paraguay, but was introduced to other areas by early Spanish explorers and settlers.

4. Lonicera sempervirens (coral honeysuckle)–again.

Lonicera-sempervirens

Although some selected cultivars of our native L. sempervirens flower on and off for much of the summer, this wild vine at the edge of my garden usually blooms only in April.  I suspect it has been induced to flower again by the unusually cool and wet weather we have been having.

5. Buddleja davidii (butterfly bush)

Buddleja-davidii

I’m keeping a watchful eye on this plant.  It volunteered in the garden and has the potential to become quite invasive in our climate, but so far I have not found any more seedlings.  I keep it around, despite its large size and ungainly branches, because butterflies adore the flowers.  Some years, it is completely smothered in several species of swallowtail butterflies, but this year there are hardly any around.  I wonder if the wet weather is to blame.

6.  Hydrangea macrophylla ‘Bailmer’ (Endless Summer Hydrangea)

Endless-Summer

I have shown this plant before, but it is blooming particularly well this year.  Gardeners generally think that blue flowers occur when H. macrophylla is grown in acidic soil and pink flowers in neutral or alkaline soil, but the situation is a bit more complex, depending on availability of aluminum ions and the amount of phosphate in the soil.  Having blue and pink flowers on the same plant, and even on the same branches, should probably tell me something about my soil chemistry, but I have no idea what.

The Propagator is the host of Six on Saturday.  Head over there to see his Six and find links to the blogs of other participants.