Xerotherm and Xanthophyll

 

Xerotherm is a plant that thrives in a hot dry environment.

Xeric: characterized by, relating to, or requiring only a small amount of moisture.

By the late 1800s, botanists were using the terms xerophyte and xerophytic for plants that were well adapted for survival in dry environments. But some felt the need of a more generic word that included both animals and plants. In 1926 that group proposed using xeric (derived from xēros, the Greek word for "dry") as a more generalized term for either flora or fauna. They further suggested that "xerophytic … be entirely abandoned as useless and misleading." Not everyone liked the idea. In fact, the Ecological Society of America stated that xeric was "not desirable," preferring terms such as arid. Others declared that xeric should refer only to habitats, not to organisms. Scientists used it anyway, and by the 1940s xeric was well documented in scientific literature.

(from the Miriam Webster Dicitonary)

Xanthophyll: any of several yellow to orange carotenoid pigments that are oxygen derivatives of carotenes

especially : LUTEIN

The loss of green chlorophyll reveals the leaves’ underlying colors, which are mainly due to a yellow pigment called xanthophyll and an orange pigment called carotene — the same pigment that makes carrots orange.

—Beth Botts, chicagotribune.com, 14 Oct. 2019

 Yes, I got a little desperate here. What words can you come up with which begin with "X"?