Please mark your calendars to meet our special guest speaker at our February 17 ^th Evening at Peckerwood Lecture Series. Phillip Douglas, curator of woody plants at Chicago Botanic Garden, will discuss recent adventures collecting plants in Azerbaijan and surrounding regions of the Caucasus. He also is a collaborator on our Texas aspen preservation project, and we will have just returned from follow-up work in the Big Bend region in time for his talk, so hope you can come join us at 5 pm on Saturday Feb 17 ^th for the latest updates. 

The browns of freeze-killed foliage contributes warm tones and pleasing contrast to the overall composition of the perennial border.

Above: Our second dusting of snow decorating a Dyckia hybrid.

Below: Pleasing colors created when Mahonia pallida is backlit by the low winter sun.

The question we're often asked is how we fared following the prolonged freeze earlier this month. The majority of the gardens is fine, though a lot of superficial damage not otherwise seen in mild winters can look devastating. John Fairey never delved too much into pushing the limits of tropical plants, instead preferring to trial likely candidates from regions that experience similar cold and heat to find plants that always look good, or quickly rebound following our weather extremes. That said, every winter event is different, and just because something survived decades unscathed doesn’t mean the “perfect storm” so to speak, won’t inevitably test the plant’s limits. Plant hardiness recommendations should always be considered suggestions. Most focus on a plant’s minimum temperature tolerance, but various factors (not just weather related) the plant endures before, during and after the freezing event all come together in an array of combinations that dictate a plant’s response, or lack thereof. 

Above: you can hardly tell the pleasing copper color of Lindera angustifolia is simply composed of dead retained leaves!

Below: The freeze-burned leaf of Cycas debaoensis still adds great interest and color.

I have been touting late January and February as an amazing time in the garden, and I still stand by that, but the unexpected duration of freezing temperatures did create a backdrop of less green and more brown to the otherwise undamaged winter flowering stars. The flowering camellias, mahonias, magnolias, and other lesser- known winter interest plants are undamaged, and the flowering has begun, with the exception of most of the Prunus mumes that didn’t get enough chill hours last winter. Previously, I noted how the dead retained leaves of certain species, can actually create amazing highlights in the woodland garden. When the light hits it right, the retained foliage of Lindera angustifolia and American beech ( Fagus grandifolia) emit a magical copper glow that can rival the yellows and oranges of traditional fall colors. Just because the leaves on the otherwise living plant are dead doesn’t mean it still can’t offer ornamental potential in the overall composition of a well-designed garden. 

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Taken in late October, the green foliage of Populus rzedowskii contrasts against the browned leaves of surrounding native P. occidentalis.

I recently learned that likely every Mexican sycamore in cultivation, widely known under the Latin name Platanus mexicana is actually a different species altogether – Platanus rzedowskii. I am now doubtful if the “true” P. mexicana is actually cultivated in the U.S. This incorrect naming is not due to a mistake, but to past taxonomic confusion among the Mexican sycamore species prior to more recent clarification. 

This started a year ago when plantsman and landscape designer Scott Ogden was telling me about the champion Mexican sycamore in San Antonio at Trinity University, which he referred to as P. rzedowskii. I knew there were other species of sycamores in Mexico, and Scott’s comment piqued my interest about “another” Mexican species in cultivation. That conversation diverted to another subject and I didn’t get a chance to discuss in more detail with him. Flash forward a year, and I was talking with landscape designer Patrick Kirwin about a named cultivar of Mexican sycamore I had seen incorporated in one of his Austin area landscapes. He told me it was called ‘Alamo’, introduced by California’s Orange County Nursery as a selection from one of Scott Ogden’s wild seed collections from Mexico. Patrick relayed some additional information from Scott indicating that these, and everything in cultivation, were all P. rzedowskii. 

The US national champion Platanus rzedowskii

Single fruits are an easy way to discern Platanus rzedowskii

While researching to determine what features separate the two species, I found the clear answers in Kevin Nixon and Jackie Poole’s 2003 paper titled “Revision of the Mexican and Guatemalan species of Platanus ( Platanaceae).” Nixon and Poole note that sycamores in Tamaulipas and Nuevo Leon, although previously referred to in horticulture as P. mexicana, were quite different from those matching the original description of the species, which is found farther south from Hildago and Veracruz all the way down to Guatemala. Therefore, they gave the name P. rzedowskii to this form from northeast Mexico in honor of prominent Mexican botanist Jerzy Rzedowski. True P. mexicana has the round fruits held in clusters of 3 or more and trilobed leaves with untoothed margins, while P. rzedowskii has solitary fruits like our native P. occidentalis, and the leaves are 5-lobed with jagged marginal teeth. All material in cultivation seems to originate from Nuevo Leon or Tamaulipas, and otherwise matches perfectly the description of P. rzedowskii. 

Regardless of the name, this sycamore is an example of a tree superior to our Texas counterpart. While our native P. occidentalis naturally thrives here, it looks quite ugly by late summer with patchy or browned leaves due to a number of diseases and insects. In stark contrast, the Mexican sycamore remains a clean dark green well into fall. Adding to the appeal is the startling contrast of the silvery white undersides of the leaves. Unfortunately, many nurseries propagate this plant from open-pollinated seed from cultivated trees, which almost always yields hybrids with P. occidentalis that tend to be quite inferior in appearance and disease resistance, which Patrick referred to as “Tex-Mex sycamores”. Mid-summer cuttings root very easily and therefore more nurseries could only offer pure P. rzedowskii propagated from superior trees. 

Bark detail of Populus rzedowskii

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Late Winter Interest Tour

Peckerwood Insiders Tour

Saturday, February 3, 10 am

Join us Saturday to see a wide variety of hardy winter-interest plants, showing that proper plant selection can provide plenty of year-around color and interest when most people are waiting for spring. Among many surprises appearing by the day, winter blooms of various Mahonia species, Camellias, and possibly some early Magnolias, along with various colorful holly berries of species not normally seen in our area. The leafless canopy casts more light into the wooded areas, to the benefit of Trilliums and other winter growing perennials, while more broadly revealing the architectural beauty of the garden difficult to visualize in the warmer months. 

Prunus mume 'Pink Panther' 

Agave between the Pool Plaza and the South Dry Garden

Plant Collecting in the Caucasus, by Phillip Douglas

Evening at Peckerwood Lecture

February 17, 5pm Wine and refreshments

Please mark your calendars to meet our special guest speaker at our February 17 ^th Evening at Peckerwood Lecture Series. Phillip Douglas, curator of woody plants at Chicago Botanic Garden, will discuss recent adventures collecting plants in Azerbaijan and surrounding regions of the Caucasus. He also is a collaborator on our Texas aspen preservation project, and we will have just returned from follow-up work in the Big Bend region in time for his talk, so hope you can come join us at 5pm on Saturday Feb 17 ^th for the latest updates. 

There will be a pre-lecture tour at 3:30 (pre-registration required)

Oaks of Peckerwood Garden

Peckerwood Insiders Tour

Saturday, March 3, 10 am

Join us at 10 am for 1 tour learning about the oaks of Peckerwood Garden. This tour will take you throughout the garden and visit many fascinating areas and beautiful places. Adam Black will spend this time with you highlighting the best of the oaks for this season.

Topic TBA

Evening at Peckerwood Lecture

March 17th, 5pm Wine and refreshments

Topic TBA

Pre-registration is required for the tour at 3:30.

Ascending the Pinnacles Trail in the shadow of Emory Peak in the Chisos Mountains of Big Bend National Park, there is one spot that affords a distant view of a small relict population of quaking aspen ( Populus tremuloides). Being that it is better known from the high elevations of the Rocky Mountains, cool forests of the Great Lakes region and the northern Appalachians extending all the way up into Alaska, many are surprised to learn of its presence in west Texas. It has long been surmised that these are the persistent remnants of what used to be extensive forests of aspen thousands of years ago when the climate was cooler. I had noticed the trees have declined over the past two decades of my gazing at these geographic outliers, and since joining Peckerwood Garden and becoming more involved with other projects in Big Bend National Park, I decided to make it our mission to get this genetic material backed up in other locations for preservation and study. After finally studying it up close earlier this month with Populus specialist Dr. Jason Smith of the University of Florida, more fascinating questions arose solidifying the value of rescuing this germplasm for further studies in the realms of climate change impacts, biogeography, and due to its distinctive features resembling some fossil aspens, genetics studies to determine its relativity to the more northerly populations. 

Among the boulders

After discussing our intentions with supportive officials at Big Bend National Park and securing scientific collecting permits, Jason and I kicked off the New Year with a plan to collect root suckers of this population during its winter dormancy. These would be used for propagation and distribution to several botanical gardens and arboreta that maintain conservation collections. Prior to our hike up to the population, we met with David Larson, the park’s chief of science and resource management, who noted that a second population of aspen had been recently discovered in a remote area of the park. He indicated it was difficult to reach and suggested seeing it another time when we could prepare better. He also introduced us to Deb Manley, a long-term volunteer who participates in a lot of the park’s botanical endeavors. She decided to join us on the hike.  

Though the population I was familiar with was clearly visible from the Pinnacles Trail, I seemed to recall my only hike up to them many years ago as being accessed from the Laguna Meadows Trail. Everyone followed my lead up to Laguna Meadows where we would then bushwhack eastward along the north slope of the looming Emory Peak, the highest point in Texas. As evening approached, it became apparent we were still far from the population, and I was embarrassingly left questioning my recollections of what route I took more than a decade ago. Since Jason and I needed to make some progress toward our backcountry campsite, and Deb had only planned to join us for the day, we decided to part ways and meet up the following day at what Deb referred to as “bathroom rock,” the large boulder on the Pinnacles Trail near the aspen overlook that serves as a spot offering hikers privacy for reasons applicable to the name it has earned. 

Scattered white trunks of aspens along the southwest slope of Emory Peak

Looping around toward our campsite along the Colima trail, Jason announced the sighting of some distant aspens through a clearing. This was far from the long-known population on the cool, shaded north slope of Emory Peak, and was in a much harsher situation on the southwest slope. A bit more trudging through the understory led to an opening into an extensive field of giant boulders below the nearly vertical peak. Poking up through the boulders were intermittent trunks of aspen. We wondered if this was the population David Larson had referred to, despite not being difficult to access. After boulder hopping for a few hundred feet, we finally arrived at a cluster of chalky white trunks and began making numerous intriguing observations. 

It was obvious that all the larger trees had extensive fungal infections in the trunks and major branches. Jason, a forest pathologist, noted similarities in these symptoms to diseases better known in the aspens of the Rockies. Dead stumps also were present nearby, as well as 1- and 2-year-old root suckers. Aspens tend to form extensive colonies that can cover many acres, with stems rising from the spreading root systems. In this colony, it appeared that the trees were growing to perhaps 30’ tall, getting stressed and overtaken by fungal pathogens. After the trunk would die back, eventually new root suckers would find their way up through the thick boulders and start the cycle over again. The colony covered an estimated 30 acres, but individual trees were widely separated. This led Jason to surmise that the colony was already there before a rockslide event that buried them. We noted how the aspens stayed within the thick layer of boulders, and would fizzle out if they entered the surrounding open forest. It appeared they were dependent on the boulder cover, perhaps providing a microclimate keeping the root system cool and therefore allowing them to persist, despite climate stress. 

Jason Smith with some of the Chisos aspens. Note how the trunks are snaking their way up through the thick boulders.

The strange, broad leaves of the Chisos aspen are quite different from their northern counterparts.

Jason then pointed out the leaf characters, which were unlike those of typical northern aspens. Being leafless at this time of year, we were studying the dead leaves under the trees, which were very broad, had almost smooth rather than toothy margins, and were uncharacteristically thick. Some leaves even showed “humps” on either side of the petiole as if they wanted to be slightly lobed. Jason noted resemblance to some fossil aspen leaves from millions of years ago. It would not be surprising if these trees were significantly different from northern counterparts, and perhaps even a living fossil that only superficially resembles the better known quaking aspen.  

As an analogy, it wasn’t until recent years that botanists began recognizing that there is one, possibly two new species of tulip tree ( Liriodendron sp.) in the southeastern U.S. that had been under our noses all the time. Though somewhat similar to the better known northern individuals, there were enough significant differences that lead researchers to conclude that these were remnants from prehistoric times that persisted in favorable conditions, yet remained cryptic due to their similarities to the abundant northern form. A number of localized populations of other tree species in the southern U.S. with interesting features point to remnant populations persisting in restricted areas since the last ice age. Could this aspen be one of them? 

Fungal disease symptoms on declining aspens

That night, Jason and I further processed what we had observed, yelling our thoughts back and forth between our distantly separated warm tents in the freezing backcountry. He noted how it would be interesting to see if the rock slide that created the boulder field that presumably buried the aspens could be dated by geologists, giving a better idea as to when the aspens were healthier. Culturing and analysis of the stress-related fungal diseases in comparison with those better known from the northern P. tremuloides populations would be interesting. Is there a separate fungus that has persisted through thousands of years among this one isolated population, or is it a more recent introduction? Do the other Texas aspens in the nearby Davis Mountains and Guadalupe Mountains, or the few disjunct occurrences farther south in the mountains of Mexico grow in similar boulder fields, have similar stress-induced diseases, growing to a certain size, dying back and resprouting? Do the other populations also have the distinctive broad, thick, nearly smooth-margined leaves? Altogether, studies of these relict populations would be a perfect subject for studies in the rise and fall of forests as climates shift over time. 

The next morning, we continued our counterclockwise loop around Emory Peak through Boot Canyon and down the Pinnacles Trail to meet Deb at “bathroom rock.” After arriving, I realized how the previous day’s decision to access the trees from Laguna Meadows was poorly thought out, despite feeling certain that’s how I reached them many years earlier. It was an embarrassingly easy hike over to the trees which, like the population on Emory’s southwest slope, were growing in a boulder field. There were a few trees growing outside the boulder field, but as long as this patch has been here, the colony’s interconnected root system never seemed to stray far from the protective blanket of rocks. Here, less disease was noted, perhaps in a more protected location on the north slope of Emory Peak and less subjected to the harsh summer sun and heat that those on the southwest slope endure. Again, we saw the unusual shaped, thick leaves. Jason also noted in both populations how the white bark has a unique texture compared with northerly populations. Root suckers were collected from this site, completing a successful mission. 

A dead aspen and its replacement, soon to suffer the same fate.

some of the larger aspens growing among the boulder field

Unlike most poplars, which root easily from cuttings, aspen types do not. The root suckers we collected will be established in pots, and sections of their roots also will be removed and potted individually to increase the material we can share with suitable conservation collections. Those gardens and arboreta we are collaborating with are situated in USDA zones 7 through 5 throughout the country. Some like Starhill Forest Arboretum in Illinois already maintain aspen clones from throughout the U.S., but until now lacked any southerly forms. We don’t know if material from the Chisos aspen will tolerate winters in the gardens with colder winters, as the conditions in Big Bend were never that cold – zone 7 to maybe 6 at the coldest during the ice ages. Denver Botanical Garden has trouble growing aspen from the nearby Rockies long term, but perhaps this Texas form would be optimum for them. If our collections prove to prosper in zone 7 gardens like easternmost recipient Bartlett Research Arboretum in Charlotte, N.C., it also would shed light on its past environmental preferences. 

Another supportive garden on the colder extent of our partners is Chicago Botanic Garden. Phillip Douglas, curator of woody plants, will be at Peckerwood in mid-February, and we plan on revisiting the Chisos aspens in hopes the flower buds will be open and therefore shed light on how many clones are present in the two populations. Jason’s initial observations of the developing flower buds suggested both sexes present at the first site we found, but the second site may only be one clone. Though they may flower, regeneration from seed is simply not happening in the Chisos. It will be interesting to get Phillip’s additional thoughts on this southerly population that has an important story to tell.