Flower:

Flowers are at the end of naked stems that branch off at the top of the plant and from the leaf axils near the top of the plant, with 1 to a few flowers on a branch. Individual flowers from ¼ to 1/3 inch across with 5 white petals that are deeply divided to look like 10. The 5 narrow star-like green sepals behind the petals are as long as or shorter than the petals and have 3 obscure veins. There are 5 to 10 stamens surrounding the center; the tip color may be red, yellow or brown, changing color as the plant matures.

Leaves and stem:

Leaves are very narrow, ½ to 2 inches long and less than 1/8 inch wide, toothless, hairless, pointed at the tip with no leaf stem and a prominent center vein. Leaves are widest at or above the middle, but that may be very subtle and not easily seen. Attachment is opposite. The main stem is square, slender and weak, causing the plant to be less erect and more sprawling.

Notes:

Long-leaf Starwort tends to grow in clumps; its weak stems and narrow leaves usually end up looking like a tangled mess in the surrounding vegetation. There are 2 similar species, S. longipes and S. graminea. Both are uncommon in Minnesota and don't likely grow in the Twin Cities area where S. longifolia is more common throughout much of the state. S. graminea has sepals that are as long as or longer than the petals, the flowers are only at the top of the plant, and its leaves are widest near the base.