* Seven Line Poems: There are several seven-line poems forms, like the tanka (Japanese) and the septet. However, these forms often have specific syllable counts and/or thematic guidelines that aren't dictated by your description.
* "R" as the First Letter: This is purely a starting letter constraint and doesn't define a poetic form.
* Eight Letters Long: This refers to the word length of the first word, not a poetic form's characteristic.
If you're looking to create a poem with those elements, you can consider:
* Free Verse: This allows you to experiment with form and structure without strict rules. You can start with "R" and a seven-line poem.
* Creating your own form: Experiment with different rhythms, rhyme schemes, and structural elements to create your own unique form.
Let me know if you have other ideas or constraints for your poem!