Riccia

...An aquatic moss belonging to the Riccia family. It is widely distributed throughout the world, and grows in ponds and rice fields throughout Japan, but in recent years, perhaps due to the effects of pesticides, it has become quite rare in many places. The plant is leaf-like and 1-3 cm long. It grows by repeatedly branching into two branches, but the rear part gradually rots and the branches separate, increasing the number of individuals. There are seven species of Riccia in Japan, and all but Riccia appear on the soil of fields and rice paddies mainly from autumn to winter. The sporophyte of this genus has the simplest structure among mosses, with no stalk or foot, and the capsule is buried in the thallus. ...

*Some of the terminology that mentions "Riccia" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…ウキゴケ科に属する水生の苔類。全世界に広く分布し，日本でも全国の池や水田に生じるが，農薬の影響のためか，近年は各地でかなりまれになった。植物体は葉状で長さ1～3cm。二叉（にさ）分枝を繰り返しながら生長するが，後方からしだいに腐って枝が分離して個体数をふやす。ウキゴケ属Ricciaは日本に7種あるが，ウキゴケ以外は，主として秋から冬にかけて畑や水田の土上に出現する。この属の胞子体はコケ植物の中で最も単純な構造をもち，蒴柄（さくへい）も足もなく，蒴は葉状体の中に埋もれている。…

※「Riccia」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報