The Biology of Gunma, Japan (群馬県の生物学): Centaurea cyanus (矢車菊, ヤグルマギク)

Okay, so this is quickly becoming a compendium of global weeds, but alas, I haven't had a chance to explore any relatively undisturbed areas yet. This next one is a native of southern Europe and is widely cultivated & established elsewhere. As an aside, the plant is protected as an endangered plant as a part of the UK's rather different environmental protection policy. I usually don't think of exotic species as worthy of government protection, but apparently somebody must; see this link.

Anyways, I found it growing within a metre of a previously mentioned 1,500+ year old Kofun (古墳), or megalithic keyhole-shaped burial mound, which is within 50 metres or so of my apartment. They are quite common in the area, and as such this particular one only has a little sign in front of it in Japanese saying (presumably) what it is, but it's surrounded by houses and ugly apartment buildings and it sort of blends in with the landscape when you're not viewing it from above. I walked past it several times without even realising it was anything more than a somewhat strangely designed public park. Here is a GoogleMaps aerial view of the mound for those that are curious about the shape:

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The English name for this plant is blue or common cornflower, while the scientific name is Centaurea cyanus L.. "Cyanus" means "blue" while the genus name derives from the Ancient Greek "kentaurieon", an ancient plant name associated with Chiron, a centaur famous for his knowledge of medicinal plants. The plant is an important symbol for various things in European culture, perhaps most notably as the national flower of Estonia (see the Wikipedia article for more on its symbolism). Aside from its use as a cultivated plant, it also has a number of medicinal applications, it was once used for a blue pigment, and it's apparently used in Twining's Lady Grey tea blend. The name is derived from the fact that it is a weed of corn fields (corn fields in the British sense of corn, of course).

The Japanese name is 矢車菊 (ヤグルマギク), which is read as "yaguruma giku". The name translates as "arrow wheel chrysanthemum". An arrow wheel is a decorative wind mill placed on the top of a pole supporting carp-shaped streamers known as "koi no bori" (鯉幟). They are flown during what used to be a holiday on the lunar calendar called "tango no sekku" (端午の節句), which celebrated the start of the rainy season, but has since been adapted to the Gregorian calendar under the new name "kodomo no hi" (子供の日), which means "children's day". Celebrated on May 5th, Children's Day is the combination of Boy's Day and Girl's Day, which used to be celebrated seperately on 5th and 3rd of May respectively. In typical sexist fashion, they made sure to make Girl's Day a part of Boy's Day and not vice versa (the change happened in 1948). Anyways, Children's Day celebrates children's happiness and personalities, and the carp streamers topped with arrow wheels somehow express the wish for families' boys to grow up strong. I personally don't see the connection between pond scum-eating fish and the hope for boys to turn out well, but it wouldn't be the first time that something Japanese made no sense. At any rate, the arrow wheel looks quite similar to the flower that is supposedly the topic of this post (see the link to the Gunma Botanical Garden entry for a photo comparison).

Unfortunately, the current generic name "Centaurea" might not stick for this plant. Recent genetic work has shown that the genus is polyphyletic, meaning the species within it do not form a single natural group. Linnaeus, the author of this particular species as well as the genus, rather inconveniently chose Centaurea centaurium as the type species for the genus, and as that particular species is African and does not group with most of the 500 or so other species currently called Centaurea, either the vast majorit will come under new generic names, or the generic name will be conserved by changing the type specimen and the aforementioed African species as well as other oddballs will get new generic names. The plants in the genus are, generally speaking, distinguished from other members of the aster family (Asteraceae or Compositae) by their often deeply lobed leaves, their spiny or comb-like phyllaries (i.e. the leaf-like bracts below the flowers or on the buds; see the last photo), as well as floral features such as typically sterile outer florets, branched styles and tailed anther bases. This particular cornflower is distinguished from its close relatives by its non-spiny phyllaries with very fine appendages, its annual habit (check the roots; if they're very robust it's not an annual), and it's short pappi (the bristley things on the seeds). Two color forms exist, blue & pink, as well as some intermediates (see photos).