September 2020 in the Garden

For a self-guided tour, use Garden Explorer to locate plants featured in this month’s post. Select a tour in the drop-down menu.

Given that it’s often difficult to predict what might be blooming at UBC Botanical Garden more than a month after I actually pen this blog post, I thought I might focus September’s tour on some of the textural qualities of plants that might be encountered at this time of year.

Light has a great deal to do with how we perceive textures, so a sunny day will accentuate the ridges and fissures in tree bark and a dull day will bring out the various gradations of green in leaves. But leaves are also not just about green, as the foliage of Boehmeria platanifolia (false nettle) can attest to. Our Boehmeria is on the south side of the boardwalk (from where it is best viewed) in the David C. Lam Asian Garden, to the west of the giant Tapiscia sinensis (false pistache) and the (much smaller) Pseudolarix amabilis (golden larch). The leaves are dull, dark green and both bullate and coarsely serrated. Bullate means with coarse, irregular, convex, often blister-like protrusions. Adding to the texture is their distinctive phyllotaxy (i.e., the three-dimensional spacing of leaves around the stem), which is decussate. Plants with a decussate leaf arrangement have paired leaves that are at right angles to the pair below. This arrangement is characteristic of the mint and nettle families. Marginal serrations are also unusually distinctive—the individual teeth attractively exaggerated.

Further to the west is a specimen of Schefflera minutistellata, with its spreading head of palmately compound leaves. Texturally, scheffleras are immediately recognizable. In most species the digitate leaves are borne on long petioles that radiate evenly around the stems. The central leaflet is usually the largest, with size diminishing symmetrically to either side, but in this species, there are smaller “second-storey” leaflets that perch above and between the primary leaflets. Both the phyllotaxy of the leaves and leaflet arrangement maximize the horizontal space available for photosynthesis, while reducing self-shading. Note also the flower stalks developing at the tips of the branches. There is an even larger S. minutistellata at the hairpin turn on Straley Trail.

Grasses are also considered textural plants, and the Garden has a huge variety, from diminutive bunchgrasses to 10 m-tall bamboos. I’m partial to the woody grasses (bamboos), with their sturdy stems and drooping leaves. In particular, I love the patterns made by the segmented culms (above ground stems), angled branches and papery culm sheaths. One of the most attractive bamboos in the Garden is the stiffly-upright Japanese hedging bamboo, Semiarundinaria fastuosa, which holds on to its large, buff-coloured culm sheaths as the branches expand. This stately species (fastuosa means “stately”) can grow to 8 m tall with culms up to 4 cm in diameter and is an aggressive runner, as you can see by the trail of culms beside Lower Asian Way at Stearn Trail.

The clumping Fargesia robusta (giant fargesia), on the west side of the Garden Pavilion, is even more dramatic with its slender, close-set culms and more copious, whiter culm sheaths. The giant fargesia is native to western Sichuan Province and is an important food for the giant panda. But not all bamboos are panda food, nor particularly large. Pleioblastus argenteostriatus (Japanese dwarf white-stripe bamboo) forms a loose low screen of willowy culms and long, narrow, softly variegated leaves along the south side of Upper Asian Way just west of the Moon Gate. The texture of this species changes with the season: cooler weather intensifies the white striping on the leaves.

Hydrangea quercifolia (oakleaf hydrangea) is another plant with bullate leaves and coarse margins. The ample leaves are technically bullulate (bubbly), as the bumps are tiny. The leaf margin is more deeply lobed than toothed, and the stalks are covered in a suede-like vestiture of hairs. This creates an unusual combination of textures that intensifies as the season progresses (the leaf surface turning purple-red with cooler weather). There are plantings by the Arbour in the Contemporary Garden and at the west end of the Fraser Grove in the Carolinian Forest Garden.

There are plenty of example of small leaves creating interesting textures. For example, Albizia julibrissin (found by the Sanctuary Garden next to the Roseline Sturdy Amphitheatre), has leaves with tiny, pencil-eraser-sized leaflets arranged in perfect pinnate rows. In bright light, when water stressed, or as light levels drop toward evening, the leaflets fold up neatly. Picea abies ‘Little Gem’ (in the Europe Section of the E.H. Lohbrunner Alpine Garden, near the Amphitheatre entrance) has even smaller leaves. The plants have a radial phyllotaxy, like the schefflera, but at a much smaller scale. The tiny, simple, needle-like leaves are densely crowded along compact branches. With age, the plants resemble miniature undulating forest-covered mountains.

No discussion of texture in the garden should neglect tree bark, and the Garden’s trees are a particularly rich realm. Good bark often takes many years, even centuries, to develop, but there are some notable exceptions. Snake-bark maples are often touted as among the most attractive for bark effect, and we have plenty of examples in the Asian and Carolinian Forest Gardens. The thin green bark of this group of maples is photosynthetic, but highly vulnerable to physical damage or even sunburn (since all that green represents living cells). One of the loveliest is the Acer davidii (Pere David’s maple) on Handel-Mazzetti Trail near Upper Asian Way. This specimen is worth stroking for its incredibly smooth bark.

Peeling bark creates another sort of texture, and in the Australasia Section of the Alpine Garden, a number of Eucalyptus species stand out in this regard. All of them are worth a look, but Eucalyptus rubida (candle-bark) is, despite its relative youth, fast developing cracks in its thick, handsome, cinnamon-coloured bark. This will eventually degrade into fibers and irregular hanks that fall away, exposing a powdery pink under-bark.

Finally, while the undisputed champion of textural bark in the Garden has to be the venerable Pseudotsuga menziesii (Douglas fir) that we’ve dubbed the “Eagle Tree,” take a moment to consider the bark on any of the large Abies grandis (grand fir) along Upper Asian Way. At about one hundred and fifty years old, these statuesque conifers show little taper on their sturdy trunks and have few branches below 20 metres from the ground. At a distance, they look like giant columns of grey, but closer up, the bark’s flattened ridges and furrows play against each other in a subtle intersecting and overlapping dance of light and shadow. Closer still and you can see the film of tiny lichens that lines the fissures and still smaller ridges of the bark. That’s some kind of texture!

Submitted by: Douglas Justice, Associate Director, Horticulture and Collections