The Yomiuri Shimbun – February 9, 2016 – Last Thursday I timed my afternoon bike ride so that I would arrive at a high bridge just before sunset. This bridge enjoys a fairly open view to the southwest, and I had hoped to watch the setting sun sink right down on the top of Mt. Fuji. Surprisingly, several other watchers were there as well. This year the Kanto-based media has been steadily touting the beauty of the “Diamond Fuji” phenomenon, the sparkle of refracted light produced as the sun disappears directly behind the mountain.
Unfortunately, although the weather Thursday was clear and dry, by late afternoon a dense haze had settled over the western horizon. All we faithful watchers were treated to was a brief moment when the silhouette of the mountain was outlined in blazing orange. But not to worry. There will be plenty more chances to enjoy the Diamond Fuji in the weeks to come.
These chances, however, will all be from spots other than my bridge. The Diamond Fuji is actually visible over a wide area to the east of the mountain. This area is defined by the seasonal progression of the setting sun as would be seen from the top of Mt. Fuji. During the course of a year, the setting point makes a round trip along a 60-degree arc; from a spot about 30 degrees south of due west on the winter solstice, to a spot about 30 degrees north of due west on the summer solstice.
The lines drawn from Mt. Fuji to the two solstice positions of the setting sun can be projected across the Kanto region. Any spot inside these two lines is eligible to experience a Diamond Fuji twice a year. My bridge is on a line running about 23 degrees northeast from the mountain, and the Diamond Fuji appears once in early April then again in early November. Nihonbashi in central Tokyo is on this same line, and thus enjoys the same event timing. All spots on a line running due east from the mountain will experience the Diamond Fuji on the spring and autumn equinoxes.
Throughout the spring and early summer the Diamond Fuji line revolves slowly in the clockwise direction. At the same time, the blooming fronts for various wildflowers push in from the south and west. The first of these wildflowers are already busy laying out soft blue carpets along sunny roadsides and on park lawns. These are the common speedwell or o-inunofuguri.
Speedwells are tiny, low-growing flowers classified in the genus Veronica. The common speedwell (V. persica) is originally native to Europe, but over the past century has spread throughout the world. The first plants arrived here in Japan in the late 19th century, and within a few decades had spread all over the country.
The Japanese generic name for speedwells is inu-no-fuguri, which means literally “a dog’s scrotum”! This name derives from the unique shape of the hairy capsules that contain the seeds. The o in the common speedwell name means “large,” and is used primarily to distinguish this alien species from the much smaller native species inunofuguri (V. polita).
The common speedwell flowers are about a centimeter across, with four green sepals and four beautiful soft blue petals. At the center are two stamens and a single pistil. These flowers are insect pollinated. Most flowers stay open for a single day, waiting for small bees and flies to visit. If they have not been visited by evening, however, the flowers simply push their own stamens and pistil together and pollinate themselves.
This ability to self-pollinate is a strong plus for any plant that wants to live in harsh urban environments, where insect pollinators are often few and far between. Repeated self-pollination results in a loss of genetic fitness and diversity, and is eventually detrimental to the long-term survival of a population. In the short term, however, occasional self-pollination is probably an adaptive strategy for roadside weeds.
When studying small wildflowers I like to make simply color pencil illustrations that show the basic characteristics. There is also, however, another fascinating system, called floral diagrams, for recording flower structure. This system was developed by 19th-century botanists, and is designed to visually show the numbers and relative position of the flower’s reproductive parts.
Botanists like to think of flowers as constructed of four concentric whorls. The outer whorl is the sepals, which protect the flower in the delicate bud stage and may also help support the fruit afterwards. Next comes the petals, which in the case of the speedwell are designed to attract and orient insects. The two inner whorls are the stamens, which produce pollen, and the pistil, which accepts pollen and incubates the seeds.