San Miguelia

...Due to the way fossils are found, there are theories such as: (1) that the places where angiosperms originated and developed in the early stages were tropical mountains where they were unlikely to remain as fossils; (2) that early angiosperm fossils do exist, but the defining characteristics of angiosperms are developmental traits such as double fertilization, so they could not be fossilized, and that they were only recognized as angiosperms when plants with leaves identical to those of modern plants appeared; and (3) that angiosperms, as can be seen from the many horticultural varieties, are a very plastic group, and that they actually appeared in the mid-Cretaceous period and achieved an astonishing diversity in a short period of time. The oldest fossils that may be angiosperms that exist before the Cretaceous period are Furcula and Sanmiguelia , which were found in the late Triassic period. Both are leaf fossils, and it is said that the former may be the oldest dicotyledonous plant and the latter the oldest monocotyledonous plant based on the course of the veins, but this is not certain.

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

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…このような化石の産出のしかたにより，(1)被子植物が起源し，初期の発展をとげた場所は，それらが化石となって残りにくい熱帯山地であったという説，(2)初期の被子植物の化石は現実に存在するが，被子植物であることを示す決定的特徴は，重複受精のような発生学的形質であるから化石になりようがなく，現生のものと同じ葉をもつものが現れるようになって初めて，それらが被子植物であることがわかるという説，(3)被子植物は多くの園芸品種をみてもわかるように，たいへん可塑性にとんだ群で，実際に白亜紀中ごろに出現し短期間に驚くべき多様性を得るにいたったという説などがある。　白亜紀以前の化石で，被子植物の可能性のあるもっとも古い化石としては，三畳紀後期より産出するフルクラFurculaとサンミグエリアSanmigueliaがある。ともに葉の化石で，葉脈の走り方より，前者は最古の双子葉植物，後者は最古の単子葉植物かも知れないといわれているが確かではない。…

※「Sanmiguelia」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