There are two trees I can think of that leave me unenthusiastic about giving them my time here. The first is Ailanthus altissima, which causes me great consternation for its invasive presence in the Bay Area (I think of it as a weed tree), and our subject tree, Myoporum laetum, for similar reasons. Neither are particularly valuable as ornamental trees, and their negatives outweigh their positive values. This should lead readers to ask, then why include them here?
Primarily, I seek to highlight species for several reasons, not just their ornamental value. For both species, classified as invasive, designers might come across them at project sites and may need to have a heart to heart discussion with their clients about harboring such trees. On occasion, I have seen landscape architects retain them in designs, partly because of unfamiliarity with their invasive status or other problems they may have, so I will include them here to inform students and designers alike.
Setting aside Ailanthus for now, let's focus on Myoporum laetum and it its better qualities. For California's coastal gardens and landscapes from San Diego to Mendocino County, this tree with no formal common name is a mainstay in the landscape. It tolerates salt air and ocean winds, so its use as a windbreak is highly valued. We might still find this evergreen tree specified as a street tree in San Francisco, a potentially challenging location with its windy conditions and sandy soil. The balance of lush greenery with low water use is generally highly coveted where wind, salt, and drought prevail. Its leaves are uniquely dotted with glands, which make them easy to identify. But don't let the pretty polka dotted flowers fool you. Unfortunately, there are too many challenges to recommend their landscape use much further.
The California Invasive Plant Council has identified M. laetum as moderately concerning, where it has potential to spread and interrupt native landscapes. Its progress is mapped by Calflora who has documented its progression, particularly in Southern California's more mild climate. In a reversal of misfortune, Myoporum thrips, an insect that distorts new growth, is difficult to control, and leads to the decline and death of these trees, has helped to minimize the trees' invasiveness. However, we can reverse again with the introduction of a resistant cultivar, M. laetum 'WCN01', has renewed concern for invasiveness. So, these challenges need to be weighed against their high value in seaside landscapes.
From the Hawaii Department of Land and Natural Resources, the presenter refers to Naio thrips, with naio being another common name for Myoporum. This video is a quick overview of their process for reducing thrip and invasive species populations to protect Hawaii's natural resources.
facts
Botanical Name: Myoporum laetum
Myoporum: Greek, myein, to close; poros for pore: its pores close to safe moisture
Laetum: Bright, vivid, or pleasant
Common Name: Ngaio tree; false sandalwood; mousehole tree; myoporum
Family Name: Scrophulariaceae
Origin: New Zealand
design considerations
Positioning: Background, windward
Garden Themes: Coastal, Mediterranean, Drought
Uses: Windbreak, screen, street tree, informal hedge, mass
identifying characteristics
Type: Evergreen shrub or tree
Form: Round
Texture: Medium
Size: 30' tall by 20' wide; size/form may be influenced by wind conditions
Outstanding Feature(s): Foliage
Bark: Green stems when young becoming brown with age, furrowed, thick
Leaf:
Type: Simple
Arrangement: Alternate
Shape: Oblanceolate
Margin: Entire
Color: Dark green with noticeable yellow-green glands
Surface: Glabrous
Flower: Summer. Axillary cymes, star-shape, white with purple dots
Fruit: Autumn. Drupe, red-purple
cultural requirements, tolerances & problems
Sunset Zones: 8, 9, 14-17, 19-24
USDA Zones: 9-10
Light: Full sun
WUCOLS SF Bay Area Hydro Zone: Low
Soil:
Texture: Sand, loam
Moisture Retention: Well-drained. Accepts brief periods of dryness.
pH: Slightly acidic to alkaline
Tolerances: Drought, deer
Problems: Classified invasive
Branch Strength: Medium weak
Insects: Thrips, aphids
Disease: Sooty mold
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Cal IPC. "Myoporum laetum." California Invasive Plant Council, Berkeley. Accessed on October 6, 2021, from https://www.cal-ipc.org/plants/profile/myoporum-laetum-profile/.
Flora. "Myoporum laetum." New Zealand Plant Conservation Network, Manganui. Accessed on October 6, 2021, from https://www.nzpcn.org.nz/flora/species/myoporum-laetum/.
Jepson eFlora. "Myoporum laetum." The Jepson Herbarium, Berkeley. Accessed on October 6, 2021, from https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=34200.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Products. "Myoporum laetum Clean n Green ['WCN 01'] PP23,163." San Marcos Growers, Santa Barbara. Accessed on October 6, 2021 from https://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=3576.
Products. "Myoporum Thrips."San Marcos Growers, Santa Barbara. Accessed on October 6, 2021 from https://www.smgrowers.com/info/Myoporum_Thrips.asp.
Taxon Report. "Myoproum laetum G. Forst." Calflora, Berkeley. Accessed on October 6, 2021, from https://www.calflora.org/app/taxon?crn=5720.
SelecTree. UFEI. "Myoporum laetum." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on October 6, 2021, from https://selectree.calpoly.edu/tree-detail/1485.
SFTrees. "Blog." San Francisco Trees, San Francisco. Accessed on October 6, 2021, from http://www.sftrees.com/.
UC IPM. "Myoporum Thrips" University of California Agriculture and Natural Resources, California Statewide. Accessed on October 6, 2021, from http://ipm.ucanr.edu/PMG/PESTNOTES/pn74165.html.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on June 28, 2021.
Photos:
At coast: "Myoporum laetum kz6" by Kenraiz is licensed under Creative CommonsAttribution-Share Alike 4.0 International.
Flower detail: "Myoporum laetum flower" by John Game is licensed under Creative Commons Attribution 2.0 Generic (CC BY 2.0).
Leaf detail: "Ngaio leaf (Myoporum laetum), backlit" by Avenue is licensed under Creative CommonsAttribution-Share Alike 3.0 Unported.
Small tree: "Myoporum laetum - Palmengarten Frankfurt - DSC01919" by Daderot is licensed under Creative CommonsCC0 1.0 Universal Public Domain Dedication.
All photos by TELCS.