Seishitsu (正室) is the Japanese term of the Edo period for the official wife of high-ranking persons. The tennō, kugyō (court officials), shōgun and daimyōs often had several wives to ensure the birth of an heir. The seishitsu had a status above other wives, called sokushitsu (側室, concubine).
The system dates back to the ritsuryō system in the Nara and Heian periods. At the time, the main wife was called chakusai (嫡妻). The last Japanese emperor to have official concubines was Emperor Meiji.
Succession disputes between sons of the official wife and concubines were a constant source of internal, often armed conflict within houses (O-Ie Sōdō).
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction