jQuery find parent form

i have this html

<ul>
    <li><form action="#" name="formName"></li>
    <li><input type="text" name="someName" /></li>
    <li><input type="text" name="someOtherName" /></li>
    <li><input type="submit" name="submitButton" value="send"></li>
    <li></form></li>
</ul>

How can i select the form that the input[name="submitButton"] is part of ?
(when i click on the submit button i want to select the form and append some fields in it)