also: ひとは
noun
one leaf
Counts a single leaf, especially of a plant. The reading ひとは is rare and literary.
紅葉した一葉が風に舞っていた。
A single autumn leaf was dancing in the wind.
noun
one page; one sheet; one card; one photo
Only with reading いちよう
Used with the reading いちよう to count flat, thin items such as pages, sheets of paper, cards, or photographs.
アルバムに一葉の古い写真が残っていた。
One old photo remained in the album.
答案用紙を一葉ずつ配ってください。
Please hand out the answer sheets one by one.
noun
Archaic counter for a single boat or small vessel. Not used in modern Japanese.
古文書には「一葉の舟」という表現が見られる。
The expression 'one boat' can be found in old documents.
一枚 is the standard counter for flat objects (paper, tickets, plates, etc.), while 一葉 is more literary and limited to leaves, pages, photos, and similar thin items.
Compound of 一 (one) and 葉 (leaf). The reading ひとは uses the native Japanese reading of the kanji, while いちよう uses the Sino-Japanese reading. The extension to counting pages, sheets, and photos comes from the resemblance to a leaf.