City of Iron and Ivy by Thomas Kent West

In an alternate London alive with botanical magic, Elswyth Elderwood is a thorn among roses: a bristly, scarred scholar in a world of socialites. Her sister Persephone is the opposite: a graceful debutante seeking a marriage that will save their family from ruin. At least, until Persephone is murdered. Suddenly the last scion of her house, Elswyth must abandon her studies and find a wealthy husband. She is thrust into a London fueled by floromancy: hedge witches sprout nightshade from their fingertips, high-born ladies weave gowns from wildflowers... and a serial killer called the Reaper transforms his victims into plant-human hybrids. When clues suggest the Reaper is a powerful nobleman, Elswyth's search for her sister's killer and her hunt for a husband become one and the same. But she is drawn to bastard-born archaeologist Silas Blackthorn-who may have dark, twisted secrets of his own. Elswyth must determine friend from foe and lover from liar-or suffer the same fate as her siste