Nemastylis is a new-world genus in the Iridaceae family with (in 2019) five accepted species distributed from the south central United States and Mexico to Guatemala. It is part of the Tigridieae tribe. Plants have upright pleated leaves with short-lived flowers with subequal tepals without claws and long anthers that collapse spirally after shedding their pollen. The genus is named for the style branches which are divided to the base into a pair of long, thread-like arms. Many pleated-leaf irids originally placed in this old genus have been shuffled about into new genera. Species once named are now placed in Alophia, Ennealophus, Herbertia, Mastigostyla, Salpingostylis, and Tigridia or considered to be varieties or subspecies of Nemastylis tenuis.
Nemastylis geminiflora Nutt. ranges from Tennessee and Mississippi west to Texas and north to Kansas and Missouri. Known as the Prairie Celestial as it is found in grassland and prairies, it also occurs in pine woods. The bulbs are often very deep. It has 6 parted sky-blue short-lived flowers and is white at the base with yellow anthers.
The first two photos from Lee Poulsen were taken April 2004 in the Hill Country of central Texas. It was in the evening just before sunset, and difficult to get a non-blurry photo of them (the last one was taken with a flash, but it bleached the color somewhat); the flowers were starting to wilt/bunch up into a ball suggesting they only last a day. The flowers are about 1-1/2 inches (4 cm) across. The bulbs were about 2 cm in diameter and about 5 in (13 cm) deep. (It was on a friend's property; he says he's accidentally dug up a number of them when digging his vegetable garden and that they're purple. They're mixed in with larger native rainlily bulbs that bloom later in the year.) They tend to be near or under the live oak trees that cover his property. The last three photos were taken on this property in 2019 by Steve and Tracy Kriese.
Nemastylis tenuis (Herb.) Benth. & Hook.f. ex S.Watson is a small irid with narrow, pleated leaves distributed from Texas and Arizona down to Guatemala. The plants grow about 10-25 cm in height and are found in Quercus forest, grassy fields and open scrub forest. This species is very variable and has ephemeral flowers that are usually blue or violet in color but can occasionally be white. It flowers during the rainy season around the beginning of July in Mexico. The plant has a wide distribution in Mexico but is scarce. Plants of the World Online lists these infraspecifics: Nemastylis tenuis var. caerulescens (Greenm.) R.C.Foster, Nemastylis tenuis var. nana(S.Watson) R.C.Foster, Nemastylis tenuis ssp. pringlei (S.Watson) Goldblatt, Nemastylis tenuis var. purpusii R.C.Foster, and Nemastylis tenuis ssp. tenuis. Photo taken in-situ in Mexico by Dennis Szeszko.