The plants in this picture are: Kikuyu grass, Cook Pines, Desmodium, Bauhinia, and Wild Olive.
Kikuyu Grass - introduced from Kenya in 1925, this is a major pasture grass in Hawaii. It is probably the main pasture grass in both the green lush paddock and the distant dryer hills in this painting. When I was a child I heard the Parker Ranch cowboys discussing its spread. They liked it as pasture grass and related different places it had spread to.
Cook Pines were probably introduced from New Caledonia by Captain James Cook. We used to call them "Norfolk island Pines" and there is some confusion.
The trees on the distant Hokuula hill were planted in the shape of a P to represent Parker Ranch. Fortunately in my mind, the shape has deteriorated. Those were pine trees.
Desmodium (lower left) is a legume introduced for pasture forage. It gets everywhere! There are several types. Desmodium intortum, also known as greenleaf ticktrefoil, was first reported in Hawaii in 1916. Desmodium intortum is a naturalized cattle forage crop from tropical America. Locally it is often called "clover".
The flowers are Bauhinia. This plant is from Madagascar and was introduced to Hawaii in the late 1800s or early 1900s, with Joseph Rock and Dr. Lyon of the University of Hawaii distributing seeds. Hawaii has 13 species of introduced Bauhinias.
Wild Olive is the precursor to commercial olives. From Africa, it was planted as a windbreak and ornamental ,and has spread widely since the 1950s as birds enjoy the seeds. There is not as much information available about this wide-spread tree as one might expect.