Shimobashira

Shimobashira is endemic to Japan and is distributed from south of the Kanto region of Honshu to Kyushu region.   It grows in the shade of trees and around streams in forests of low mountains.

The section of the stem is squared which characterizes plants belonging to the family Lamiaceae and grows 40 to 70cm in height.   The upper part of the stem bends in a horizontal direction.   This plant has opposite leaves which are elliptic and have shallow serrations.   It is thin, soft and has fine hairs on the vein.

The raceme expands upwards from the axil at the upper half of the stem.   From September to October, white flower of 7mm in length blooms.   It is labiate corolla; the upper lip is shallowly split into two part and the lower lip is shallowly split into three part.   The flower blooms, alternating in pair, at right angles.   The flower of Shimobashira is not significantly different from usual plants belonging to the family Lamiaceae, so that it does not attract interest in particular.   However, in early Winter, in the cold morning when a pond begins to freeze, thin sheet-like ice crystals form from the surface of the stem which sheds its leaves and white ice-flowers bloom at the base of the stem to attract people.

Since this plant forms ice structures resembling a frost column, it is named Shimobashira, meaning frost column, in Japanese.   The genus name, Keisukea is associated with the name of Japanese botanist, Keisuke Ito (1803 - 1901) in Meiji Era who is known for creating the words, stamen, pistil, pollen, etc. in Japanese.

The phenomenon which ice-flower blooms is not related with a plants life but is purely a physical phenomenon.   Namely, it is the phenomenon which an aperture is formed between vascular bundle and, pith and cortex, in the dead stem.   Water rises in the aperture by capillary phenomenon, and the water is frosted on the terrestrial part to form the frost column.

There are some plants which form the frost column; ex.

Plectranthus effusus Plectranthus, Plectranthus kameba (Lamiaceae)

Pertya robusta Beauv. (Asteraceae)

Polygonum filiforme Thunb. (Polygonaceae)

Achyranthes japonica Nakai (Amaranthaceae)

Parasenecio delfiniifolia (Siebolt et Zucc.) H. Koyama (Asteraceae)

Lysimachia clethroides Duby (Primulaceae)

Classification: Lamiaceae Keiskea
Scientific name: Keiskea japonica
Japanese name: Shimobashira
English Name: ---
Native locality: Japan
Ecological description: Perennial
RDB : ---
Planting place: Japanese Garden
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