Petrusa B. Van Rhijn was the daughter of Petrus B. Van Rhijn, businessman and member of the Cape Legislative Council, who founded Vanrhijnsdorp (which was named after him) on his farm in 1887. Petrusa married Evert Rood and eventually had ten children, but nonetheless played an active role in social and political life. She was a keen collector of seeds, succulents and bulbous plants, which she sent to botanists such as N.E. Brown* at Kew Gardens in England, I.B. Pole-Evans* in Pretoria, N.S. Pillans* in Cape Town, and T.N. Leslie* in Vereeniging. Many of the plants she sent to Pretoria were illustrated in the early volumes of The Flowering Plants of South Africa (1921-1944). The genus Roodia and the species Punctillaria roodiae and Rimaria roodiae were named after her by N.E. Brown. Other species that commemorate her are Lachenalia roodiae, Veltheimia roodiae and Pleiospilos roodiae.
Some years after her husband's death she married J. Lambrechts of Ceres. After his death she settled in Vanrhijnsdorp.