People ask: “What is your favourite plant?” “Favourite flower?” “Favourite fern?” “Favourite tree?” No one ever asks about your favourite branch, but here’s mine.
The overall shape and habit of a plant is determined by only a few factors. Genetic factors are foundational; barring a mutation of some kind, any member of a species will look similar to other members. How the genetic factors are manifested in the physical individual, though, depends in large part upon the environment.
Phenotypic plasticity is the ability of an individual organism to respond to environmental factors. Being sessile, plants generally have elevated abilities to physically differ in shape and habit from one another in comparison to mobile organisms, like animals. For example, take two clonal magnolia plants (genetically identical) and plant one in shade and one in moderate sun. Assuming both survive (and all other factors being equal), it is likely the shade-grown plant will have longer (but weaker) branches in comparison as the branches undergo etiolation in an attempt to gather more light for photosynthesis and, therefore, growth. Grow the same two plants in similar conditions and it is likely they will grow at similar rates and achieve the kind of uniformity one often sees in properly-spaced street trees.
Returning to today’s photograph: it is likely that there is a genetically-determined (and physically manifested via hormone production) minimum branch length between buds/nodes in order to ensure that the flowers are not so close together as to interfere with each other. The photograph is a two-dimensional representation of the three-dimensional scaffolding, so you’ll have to use your imagination and “see” the spacing in what otherwise look to be overlapping flowers.
This Sargent magnolia grows near the entrance to “The Tunnel” in the David C. Lam Asian Garden, here at UBC. When I last checked on this plant on Thursday, the terminal flower buds were not showing any colour. I suspect it’ll be at least a week before it looks like this, though many of the garden’s magnolias seemed to accelerate into full bloom over the past (somewhat) sunny weekend.
Magnolia sargentiana, native to China’s Sichuan and Yunnan provinces, is listed as vulnerable according to the IUCN Red List. The good news is that it was previously listed as endangered. However, its improvement in status was not due to conservation efforts but rather a comprehensive survey determining there were more extant individuals than previously thought, as noted:
It was thought that only around 40-50 trees of Magnolia sargentiana remained in Yunnan but Global Trees Campaign field surveys in April 2006 recorded 12 sites with a total population estimated at about 20,000. A Sichuan University/University of British Columbia Botanic[al] Garden team recorded extensive and protected populations in two of four main reserves in the Dafengding region of southern Sichuan covering at least 60,000 ha of mixed evergreen/deciduous forest, during fieldwork in September 2006.