Texas Wildflowers: A Field Guide, Loughmiller, Campbell and Loughmiller, University of Texas Press. 2018
Website with various books for download on Texas Hill Country Plants-
Guide to Identifying Texas Milkweeds-   Identification of Milkweeds in Texas
Milkweeds Xerces Society- Milkweeds: A Conservation Practitioner’s Guide | Xerces Society 
Bluebonnets- Bluebonnet FAQLady Bird Johnson Wildflower Center

Wildflowers of the Texas Hill Country- Enquist, Lone Star Botanicals, 1987

Wildflowers of Texas- Eason, Timber Press Field Guide 2018

Wildflowers of Texas, Ajilvsgi, Shearer Publishing. 1984

Southwestern and Texas Wildflowers, Niehaul, Ripper and Savage, Houghton/Mifflin. 1984

Wild Orchids of Texas, Liggio and Liggio, UT