Number five in a series featuring photographs and writings from other staff and researchers at UBC Botanical Garden and Centre for Plant Research. Like yesterday's photograph, this image is by David Tarrant, UBC BGCPR's Public Relations and Programs Coordinator, from a recent trip to New Zealand. – Daniel
In his notes to me for this entry, David wrote, “These cypress knees were taken in Ayrlies, the amazing garden of Beverley McConnell. The garden is located in Whitford, just south of Auckland.”
Unlike yesterday's and tomorrow's plants, bald cypress is not a native to New Zealand. Taxodium distichum is instead native to the southeastern United States, Mexico and Guatemala, but is also widely cultivated.
Why do the roots form knees? Despite speculation that the knees help provide oxygen to the roots in water-saturated soils, no physiological function has yet been determined (source: the “Silvics of North America” account for Taxodium distichum). Knees of mangrove trees, however, do promote the diffusion of oxygen into the roots. What's the difference? Mangrove roots forming knees have lenticels, recently discussed in the BPotD entry on Prunus serrula. Taxodium distichum? No lenticels.
For more on this beautiful tree (including photographs), see Taxodium distichum via the Gymnosperm Database on conifers.org.
Botany resource link: About Plant Physiological Ecology (an introduction to the topic) – “The problem of how plants can grow in places representing severely unfavorable climate conditions and growth substrates is central to physiological ecology.”