Hop hornbeam makes me happy

At the end of my first week at Kew, all the interns were taken to the library.  As Daisy and I walked toward the entrance of the building, one tree stopped me in my tracks.  The tree was completely draped with lacey white clusters of seed pods.  "What is that tree?" I asked Daisy, assuming it was an English native.  She didn't know, but I kept my eyes peeled for another specimen with a label.

Beautiful, showy seed clusters of Ostrya virginiana
resemble hops, thus the common name "hop hornbeam"

Later that summer I noticed another specimen growing in Kew's Duke's Garden.  The label identified it as Ostrya virginiana (1973-14189), more commonly known as ironwood or the hop hornbeam.  Imagine my surprise to learn that this tree is native to my region of North America, and then some.  Hardy to USDA zones 3 to 9, its range spreads as far north as Prince Edward Island and Manitoba, westward to the Dakotas, and as far south as Honduras. 

What the hop hornbeam lacks in flower luster, it makes up for in seed.  The green catkins aren't really that noticeable or attractive, but the seed pod clusters are very attractive and persistent.  These clusters resemble hops, which earn the common name "hop hornbeam".  The specimens at Kew have held their clusters from at least the last week of June until present.  The seed pods were a brilliant white at the end of June, fading to salmon, now with tinges of brown.  The seeds are a food source for wildlife including birds and small mammals.

View of the attractive clusters
from inside the tree

Although the tree is stunning in seed, it is also attractive in foliage.  The shiny green leaves resemble an elm or birch.  Fall foliage is yellow.  I've seen specimens with a very fine, gold fall color that persists for several days.  The autumn show may not be dependable and will vary by the environmental conditions.  According to the Missouri Botanical Garden plant finder website, "Leaves turn an undistinguished yellow in autumn and often drop early."

Ostrya virginiana is a slow growing, medium sized tree.  In most regions within its range, this tree won't get taller than about 40 feet.  There may be some exceptions, such as the 73 feet tall by 88 feet wide specimen discovered in Michigan in 1976.  But achieving such heights would take a great deal of time.  Its slow growth results in very dense, hard wood (thus the common name "ironwood").  However, this feature is not of much economic value because it would take such a long time for a stand to yield any harvest worthwhile value.  

Yet the slow growth, small stature, and strong wood makes this tree a valuable addition to a residential or commercial landscape situation.  Businesses and homeowners should consider substituting this underused strong, healthy native for the more common pest and disease prone Cornus florida or extremely weak-wooded and invasive exotic Pyrus calleryana 'Bradford'.

Despite the great potential for cultivating Ostrya virginiana in the urban environment, it has been classified as a "weed" by those who cultivate timber crops in some regions.  To quote a USDA Forestry report from 1990:

Attractive foliage

The slow growth and small size of the species earn it the title "weed" throughout its range, especially in some areas in the South where it is considered the number one weed species. Eastern hophornbeam usually is discriminated against in stands managed for timber. Silviculturally, more interest has been given to eradicating it than to improving its growth.

Perhaps the hop hornbeam is a bit weedy in stands of timber because it is so adaptable.  Ostrya virginiana has been found in soils that have acidity levels between 4.2 and 7.6 pH, and growing in elevations between 250 feet and 5,000 feet.  The hop hornbeam is also very pest and disease resistant, with few recorded issues.  One thing this tree won't forgive is wet feet.  In the wild, it is common in dry stream beds, bluffs, and even xeric conditions. 

Fall is approaching, and the upcoming cool season is a fantastic time to add woody trees and shrubs to any landscape (learn more by reading the tree planting post).  When considering what specimens do add to your garden, be sure to add the adaptable and beautiful Ostrya virginiana to the list. 

If you have any questions, comments or suggestions, please feel welcome to leave a comment or send me an email.

To see more photos from this week, be sure to check out the album "Hop hornbeam makes me happy" on the Plante on Plants Facebook page.  "Likes", shares and comments are appreciated.

Nice, open habit

Shaggy, peeling red bark

All photos and videos were taken by Amanda Plante at the Royal Botanic Gardens, Kew unless otherwise stated in the caption.

Sources:

• Center for the International Trade in Endangered Species database
• "Ironwood or Hop Hornbeam".  N.D. Tree Handbook.  North Dakota State University.
• Kew's Living Collections database
• Metzger, N.F.  (1990).  "Eastern Hop Hornbeam".  Silvics of North America, Volume 2: Hardwoods.  United States Department of Agriculture Forest Service.
• "Ostrya virginiana".  Missouri Botanical Garden Plant Finder. 
• The International Union for Conservation of Nature and Natural Resources Red List of threatened species
• The Plant List website
• The Royal Botanic Gardens, Kew website and staff

Giants in the Conservatories, Victoria amazonica and cruziana

Introductory page to Twelve Views of
Guiana.  Note the V. amazonica in the
water. (Schomburgk, 1841)

Several years ago when I was just getting started in horticulture, I was flipping through a textbook and saw an old photo of a child standing on a massive lily pad.  The caption read something like, "Child supported by foliage of Victoria amazonica".  I thought to myself, "I'd like to see that."  And this week I finally did.

Kew currently cultivates two species of giant waterlily, both of which are in the waterlily family Nymphaceae.  Victoria amazonica (2007-1804, KKNO), formerly V. regia, grows in the Princess of Wales Conservatory and V. cruziana (2011-1436, HSIK) in the Waterlily House.

Discovery and Present Range

According to Ray Desmond in The History of the Royal Botanic Gardens Kew, V. amazonica was first seen by a European, a botanist for the Spanish government, in 1801 in Peru. Subsequently, botanists from France spotted the species in Argentina in 1828, a Germany botanist found it in the Amazon in 1832, and Robert Schomburgk found it on the River Berbice in British Guiana in 1837.  Schomburgk shared parts of the plant that he collected and drawings with John Lindley (who had an influential role in keeping Kew intact during a turbulent period in its history).  Lindley named the plant Victoria reggia after Queen Victoria (Desmond, p. 178).

Tom and Tiffany prune and remove flower buds from
V. amazonica in the Princess of Wales Conservatory

V. cruziana inhabits a similar region, with a range from Paraguay to Northwest Argentina.  Both of these massive waterlilies can be found today in South America near Bolivia.  Neither of these species have been assessed by the IUCN for any threats to their existence in the wild.  Furthermore, CITES did not list either Victoria in their endangered species database.  Although those organizations have not listed these as threatened species, the environment they are native to could be damaged by climate change and human development.

Cultivation at Kew

Victoria amazonica was first cultivated at Kew in 1846, when twenty five seeds were bought from a collector from Bolivia.  Only two of the seeds sprouted, but they died shortly afterwards.  The issue seemed to be how the seeds were transported from Bolivia to England.  The first shipment had been packed it clay, and the next two were packed in soil in a Wardian case, dry capsules.  A fourth shipment of seeds packed in clean river water that arrived in 1849 was more successful.  That season Kew was able to raise 50 plants in a large tank in one of the glasshouses.

Visitors from around the globe stop in the
Waterlily House to inspect V. cruziana

At that time, several gardens in the area were essentially competing to see who could coax the first flower.  While the specimens at Chatsworth and Syon house were blooming, Kew's attempts were unsuccessful, possibly due to the poor quality of the Thames River water.  The first Victoria amazonica bloomed at Kew in June 1850.

The popularity of the giant water lily inspired Kew's director at the time, William Hooker, to commission a new building to house and display these finicky plants.  They completed the structure, today known as the Waterlily House, in 1852.  However, V. amazonica did not thrive, and was moved to another house (Desmond, p. 179).  Today you can find V. cruziana growing there in its place (Desmond, p. 313).

It is interesting to note that the V. cruziana growing at Kew wasn't the original collection.  Kew lost all specimens of this plant during World War II.  At that time, the conservatory at the University of Helsinki was damaged during a bombing.  Helsinki's V. cruziana survived the attack, and the progeny were sent to Kew, where they have been cultivated in the Waterlily House since 1999 (Desmond, p. 358)

Characteristics

Foliage

As is true of many plants, the foliage of Victoria unrolls as it opens.  The underside of both V. amazonica and V. cruziana is covered in sharp spines.  The prickly spines beneath the opening leaves gives a strange, otherworldly appearance to the new growth.  These spines help prevent the leaves from being eaten by hungry fish, which would negatively effect how the foliage functions.

Unfurling new growth of V. amazonica

You see, in addition to spines, there are also deep ribs underneath the massive lily pads.  These ribs hold air beneath the pad to keep it buoyant.  They also provide structural support, like the frame of a house.  Enough strength, at times, to support the weight of a small human.  So if a grazing fish were to nibble too much of the foliage, this would compromise the strength of the leaf and its ability to stay afloat.

Another interesting fact about Victoria leaves is that the foliage will grow to the size of the container.  When I asked Silke, who works in the Waterlily house about the feasibility for growing V. cruziana at home, she concluded that it would be possible, but difficult.  And if placed in the size pond that is regularly found in a home landscape, the foliage wouldn't be much larger than that of any other lily pad.

Differences

Although the leaves of V. cruziana
(above) are smaller than V. amazonica,
it has a much taller lip.

So what's the difference between the foliage of these two giants?  For one thing, V. amazonica tends to produce larger leaves.  The foliage of V. amazonica can reach 2.5 meters in diameter, while the diameter of V. cruziana's leaves usually maxes out closer to 2 meters.  But these statistics don't stop a little friendly competition between staff in the Waterlily House and the Princess of Wales Conservatory. 

This year, the staff competed to see who could produce the largest lily pad by a certain date. Silke in the Waterlily house told me that her group had lost the competition because they got a later start.  I asked Tom, an apprentice, and Tiffany, a staff member, in the Princess of Wales Conservatory about the wager.  Tom grinned and said, "Yeah, it wasn't even close."

Although the foliage of V. amazonica may grow larger than V. cruziana, the edge of the pad is not as tall.  While this may not seem that important at first, a tall edge is crucial to prevent other leaves that would compete for sunlight from sliding on top of the pad.  This lip can also be more aesthetically appealing.  It provides more of a reflection on the water, and is really lovely when the sunlight shines through.

Flower

Unopened V. amazonica flower bud, held by Tom, an
apprentice in Kew's Princess of Wales Conservatory

Both species have large, creamy white flowers that open in the evening and are pollinated by beetles. Even though both giant waterlilies are starting to set flower buds at Kew, you won't see any on display until later in the year.  When I arrived at the Princess of Wales Conservatory, Tiffany and Tom were pruning out the prickly buds to compost.  The reason why is that if allowed to flower, the plants' energy would go into flowering, fruiting, and setting seed rather than growing large leaves.  People come to Kew from all around the world to see these massive lily pads, so Kew does their best to produce big ones.

However, the species in cultivation at Kew are allowed to flower later in the year, because the seed is vital to producing the next season's crop.  Neither V. amazonica or V. cruziana will reliably overwinter at Kew, even if provided the best possible environment.  So, staff pollinate the flowers by hand, store the seeds in water, and start new seedlings early in the year and grow them on in the Tropical Nursery glasshouse so when they are ready to move they are large and ready for visitors.

Cultivation

Tom disects the unopened flower bud
of V. amazonica so we can inspect
the anatomical features

Although both species of Victoria thrive at Kew during the warmer months, both begin to decline in the fall.  This makes sense, because both plants are native to the tropics of South America.  For interested readers in the US, their USDA Hardiness Zones are 10-11.  For readers in the UK and beyond, that means they can tolerate a minimum temperature somewhere between 4 and 11 degrees Celsius.  Measures could be taken to overwinter the plants, but the effort would require very specialized environments with specific heat, supplemental light, and water requirements.  Instead, Kew treats these plants as annuals rather than temperennials.

In Kew's online profile of V. amazonica, they note that aphids can be a problem at times.  They try to reduce pest and disease pressures by keeping the plants healthy and happy by adding plenty of fertilizer, growing in a large enough pot, and regular pruning.

A Sight Worth Seeing

Before leaving the Princess of Wales Conservatory, I took a moment to stand back and take in one last look of those giant leaves.  An older gentleman had pushed his father in a wheelchair to the water's edge while I'd been speaking to Tiffany and Tom.  "What do you think of it?" I asked.  "I've never seen anything like it," the father responded. "Neither have I."

If you have any questions, comments or suggestions, please feel welcome to leave a comment or send me an email.

Victoria amazonica can be seen in Kew's Princess of Wales Conservatory

Kew's Victoria cruziana is on display in the Waterlily House

All photos were taken by Amanda Plante at the Royal Botanic Gardens, Kew unless otherwise stated in the caption.

Sources:

• Center for the International Trade in Endangered Species database
• Desmond, Ray.  (2007).  The History of the Royal Botanic Gardens Kew (2nd Edition).  London: Kew Publishing, Royal Botanic Gardens, Kew.  177-179, 345-346.
• Kew's Living Collections database
• Missouri Botanic Gardens plant finder database
• Perennial Resource glossary
• The International Union for Conservation of Nature and Natural Resources Red List of threatened species
• The Plant List website
• The Royal Botanic Gardens, Kew website and staff
• Schomburgk, Robert H. (1841).  Twelve views in the interior of Guiana from drawings executed by Mr. Charles Bentley, after sketches taken during the expedition carrier on in the years 1835 to 1839, under the direction of the Royal Geographical Society of London, and aided by Her Majesty's government with descriptive letter-press.  Retrieved from The New York Botanical Garden Mertz Digital Collections.