Contributed by Brigette Brown

The canopy above shifts from vivid greens to gilded yellows and browns. Below, the understory is carpeted in a blanket of fallen leaves. The wind whispers through the branches. Another crack and thud off in the distance: the sound of acorns dropping and tumbling all around. Autumn’s arrival in the woods.

Not all trees create acorns. An acorn is simply the nut of trees in the genera Quercus, otherwise known as oaks, and some close relatives as well. Shape, size, color, and structure of the acorn will all depend on the specific type of oak. These differences create a wide variety, such as the warty scales and greenish tint of white oak (Quercus alba) acorns to the small, shallow, and dark willow oak (Quercus phellos) acorns. These nuts will mature on a tree anywhere from six months to over a year. Some will have wooly hair on the inside of the shell, others will be smooth as bark. And some will be bitter, full of tannins, while others are nutty and great for roasting.

From late August to November as acorns drop and cover the ground, they become ‘mast’ an important food source to wildlife as well as humans. Birds, squirrels, mice, deer, and weevils all consume raw acorns as a primary part of their diet. Domestic pigs gorge on acorns in farmer-controlled, agroforest oak groves in places such as Spain, Portugal, and southern England. Humans however generally need to prepare this nut for consumption. In Yosemite Valley, California, the intricate preparation of black oak (Quercus kelloggi) or tanbark oak (Notholithocarpus densiflora) acorn is an integral part of the Miwok/Paiute people’s tradition.

"Tender germ, of oak an acorn Whence the beauteous plant sprang upward,
And the sapling grew and flourished..."
-The Kalevala, trans. W.F. Kirby

The acorn, and the oak, hold great significance in many cultures around the world. For thousands of years, ships, furniture, and buildings were all were produced using oak wood. Oak trees also feature prominently in mythology, from the felling of Ceres’s mighty oak in Ovid’s Metamorphoses, to the planting of the oak tree of Jumala in The Kalevala, Finland’s national epic. During the industrial era, city-bound nature enthusiasts began ‘forcing’ acorns on water with specially-made acorn vases and glasses. Now, this tree makes up a substantial proportion of our woodlands in the northeast. There are over 500 Quercus trees at Morris Arboretum, and many of them planted as acorn or sapling.

This October, create a small oak woods in your own home. Look for acorns with a rich, healthy coloring, and perhaps a crack in the outer casing. Look for small holes as well, and cast those off. Soak your gathered nuts for 24 hours, and any that float should be tossed back outside for the birds and squirrels. Those that sink, place in a bag with a moist paper towel for a few weeks in the refrigerator. Look for growth. Afterwards, find a small vase with an opening to rest the acorn on. Fill with water just to the tip of the acorn, and top it off as the water evaporates. Place on sunny, warm windowsill. If all goes well, the acorn will continue to crack open, the roots will grow downwards to the water, and the sprout will grow upwards. The acorn can live in this environment for up to a year, and then should be planted outside.


Contributed by Katherine Wagner-Reiss

Oxydendrum arboreum was named for its sour-tasting sap. The species name combines the Greek roots oxy, “sharp, sour” and dendrum, “tree” and the Latin specific epithet arboreum, “tree-like.” It’s in the heath family, Ericaceae, which also includes blueberries.

The common name “sourwood” reflects the fact that the chewed leaves taste sour; this is due to oxalic acid. Another vernacular name is sorrel tree: the leaves taste like sorrel, the common name for various herbs that also have leaves with a sharp taste because of oxalic acid. A third common name is lily of the valley tree because the racemes of dangling white flowers are visually reminiscent of lily of the valley.

Bees use the nectar of these sweet-smelling flowers to concoct the delicacy sourwood honey. Carson Brewer was an American conservationist in the Appalachian Mountains where this tree, native to the Eastern US, grows most abundantly. According to Brewer: “Most honey is made by bees. But sourwood is made by bees and angels.” Sourwood honey is available for sale online, if you want to try some!

Oxydendron arboreum is also used as an ornamental tree for its many fine attributes: 1) The white flower sprays are lovely both when they bloom against a background of green summer leaves and after they mature to silvery capsule-type fruits that contrast with the red autumn leaves. 2) The fall specimen holds it reliable crimson red leaves up to six weeks. 3) The narrow crown and moderate height in cultivation (25’-30’) make it suitable for smaller landscapes.

The Morris Arboretum has four of the straight species Oxydendrum arboreum. Two of the trees were part of the original Morris estate. Find the locations of all four at Collection Connection.

The sourwoods will be easy to spot this fall as they call attention to themselves with their early and long-lasting flaming leaf displays.

Katherine has her Certificate in Botany from the New York Botanical Garden and is a botanical tour guide and freelance writer.

Oxydendrum arboreum: Note that the white flowers face downward. After pollination, the individual flower stems (pedicels) turn, so that the resultant fruits face upward with persistent pointed styles. Photo by Katherine Wagner-Reiss.

Oxydendrum arboreum 1932-0018-A: Notice the characteristic blocky pattern of the bark with focal exposure of a reddish-orange inner layer at arrow. This tree from the Morris estate is between the main parking lot and the Visitor Center.  Photo by Katherine Wagner-Reiss.

Oxydendrum arboreum: Notice the silvery fruit capsules contrasting with the red leaves in autumn. Photo by Katherine Wagner-Reiss.


Contributed by Anthony Aiello, The Gayle E. Maloney Director of Horticulture & Curator

The Arboretum regularly participates in domestic and international plant exploration and currently I am in the second week of a collecting trip to the main Island of Honshu, Japan.  This trip is a follow-up to last year’s and while we are revisiting one of our locations, we are also exploring other areas in search of our target plants.  I am joined by Steve Schneider of the Arnold Arboretum of Harvard University and Ian Jochems of Polly Hill Arboretum (Martha’s Vineyard) and led by two collaborators from Utsunomiya University, Mineaki Aizawa an his graduate student Tatsuhiko Shibano.  

Last week we started out collecting in Wakayama prefecture, in southwestern Honshu, staying at the Hokkaido University Forestry Station where we ended last year’s trip. The goal was to find the species that we missed last year, or re-collect ones where we had found only a small amount of seed or others which did not have much germination.  We were collecting selectively, but were excited by finding horticultural interesting plants such as the wheel-tree (Trochodendron aralioides), umbrella-pine (Sciadopitys verticillata), and anise magnolia (Magnolia salicifolia), among others.  

Our next stops were slightly further east where we were looking for very specific azaleas, found only in a few locations in Japan.  Still in Wakayama, on Mount Kasaneyama we came across Weyrich azalea (Rhododendron weyrichii) and rose azalea (R. reticulatum), two of the so-called three-leaved azaleas because of their whorled trios of leaves at the end of the current year’s growth.  Among the three-leaved types are the more familiar royal azalea (R. schlippenbachii) and one of my favorite plants at the Arboretum, the Mt. Amagi azalea (R. amagianum) which can be found in the Garden Railway with flowers in early June.  

Our next stop was on Sugashima Island, a small island at the mouth of Ise bay on the south coast of Honshu.  We were looking for yet another of the three-leaved azaleas, the shrine azalea (R. sanctum) and a plant familiar to many Arboretum readers, the white enkianthus (Enkianthus perulatus).  After a 15 minute ferry ride, we arrived in a small fishing village and proceeded to hike towards the summit of the island, Mount Oyama.  Along the way we found our two targets growing side by side along with Japanese little leaf boxwood (Buxus microphylla var. japonica)

After returning to the mainland that afternoon, we were fortunate to visit the holiest shrine in Japan, Ise Jingu, the namesake of the shrine azalea that we had collected earlier in the day.  It was from here that this species was first described in the early 1930s..  

From there we have travelled back through Tokyo to the city of Utsunomiya, about one hour north of Tokyo by bullet train.  Here we will make further excursions to two locations to the west, hoping to find the remainder of the target species for our expedition. Once the seeds that we have collected are safely back in the U.S., they will be grown by our propagator Shelley Dillard, and eventually planted throughout the Arboretum.  It is through this process that we continue to grow our collection, adding to its diversity and scientific value.

Contributed by Luke Hearon, The John J. Willaman & Martha Haas Valentine Plant Protection Intern

Saddleback Caterpillar with pupating young of a parasitoid wasp
saddleback caterpillar (Acharia stimulea) hosting some very unwelcome guests (Cotesia sp.).

While not particularly rare in the eastern half of the U.S., the saddleback caterpillar (Acharia stimulea) has long been on my bug-seeing bucket list. I do wish I had encountered the caterpillar under different circumstances; the caterpillar came to my attention because our Martha J. Wallace Plant Propagation Intern, Emily Conn, accidentally touched it while doing garden work. When it meets your skin, the saddleback caterpillar is impossible to miss and difficult to forget. Those black-tipped bristles that adorn the insect are precisely the reason why this caterpillar wears its flashy and memorable bright green saddle. These spines bear a powerful venom. On contact with skin, the spines deliver this venom and may break off deep under the surface, increasing the pain and duration of the “sting.” Already comparable to a wasp sting, if the spines cannot be removed, the burning pain intensifies and persists. It’s a potent reminder that the more striking the insect, the less readily it should be handled.

Of course there are another few dozen subjects of these photos: the parasites. The pale cocoons blanketing the caterpillar are the pupating young of a parasitoid wasp in the family Braconidae, and likely the genus Cotesia. A warning before I proceed: what follows is not for those who anthropomorphize caterpillars, nor for those who have recently eaten a meal. If you’re fond of the movie “Alien,” proceed.

Saddleback Caterpillar with pupating young of a parasitoid wasp
saddleback caterpillar (Acharia stimulea) hosting some very unwelcome guests (Cotesia sp.).

While technically a type of parasite, the term “parasitoid” is essential to distinguish the modus operandi of these killers. As conventionally understood, a good parasite preserves its host. If your existence is dependent on the life of another, it seems to follow that it is evolutionarily disfavorable to kill that other. Insects have a clever way of circumventing this evolutionary law. The parasitic larvae indeed want the caterpillar to stay alive; the full grown adults, however, are indifferent. Once the larvae complete their development, the wellbeing of the host is irrelevant. A parasitoid does preserve its host, but only so long as it is using it. Thus, the parasitoid inhabits the gruesome space between the conventional parasite, which never kills its host, and the conventional predator, which kills its prey relatively instantaneously. The parasitoid kills, and kills slowly.

As humans, the parasitoid concept may seem utterly alien, a thing out of fiction. The reality is, parasitoid wasps, flies, and even a few beetles represent a massive amount of terrestrial biodiversity. A recent speculative, but rigorous, paper gives a few calculations of the total number of species of parasitoid wasps. Their conservative estimate? 833,590 species. Even if this titanic estimate were many times greater than the true diversity of parasitoid wasps, it has become increasingly obvious over the course of recent study in this field that these wasps are far more earthly than alien.