A Light and Electron Microscopic Study of the Palo Verde Tree of the Desert Southwest

ISSN: 1937-9056 Copyright © 2018 Answers in Genesis, Inc. All content is owned by Answers in Genesis (“AiG”) unless otherwise indicated. AiG consents to unlimited copying and distribution of print copies of Answers Research Journal articles for non-commercial, non-sale purposes only, provided the following conditions are met: the author of the article is clearly identified; Answers in Genesis is acknowledged as the copyright owner; Answers Research Journal and its website, www.answersresearchjournal. org, are acknowledged as the publication source; and the integrity of the work is not compromised in any way. For website and other electronic distribution and publication, AiG consents to republication of article abstracts with direct links to the full papers on the ARJ website. All rights reserved. For more information write to: Answers in Genesis, PO Box 510, Hebron, KY 41048, Attn: Editor, Answers Research Journal. The views expressed are those of the writer(s) and not necessarily those of the Answers Research Journal Editor or of Answers in Genesis. Introduction The palo verde tree (well known to residents of Texas, Arizona, New Mexico, Mexico, as well as Central and South America) has bright green trunks, stems, and leaves and is perfectly fitted for life in the harsh Southwest. The bright green nature of the trunk, stems, and petioles of Parkinsonia is undoubtedly the reason why this tree is known as the palo verde (“green stick” in Spanish). It is extremely drought tolerant, thrives on little water, and is even considered a weed in many communities. It is drought deciduous, meaning that it drops its leaflets during certain, particularly dry periods, and it also employs stem photosynthesis, which means that most photosynthesis takes place in the petioles, stems, and trunk, and not in the leaves. Palo verde has variants found on Hawaii, the Galapagos Islands, and southern Africa, as well as in India. In Australia, where it was introduced as an ornamental and shade tree in the year 1900, it has become a widely spread invasive, requiring the introduction of several insects to serve as biological controls to limit further spread. Palo verde has also been reported from the Caribbean as well as Central and South America. In Florida, it is prized as an ornamental. In 1966, it was named the city tree of Miami. The palo verde was also made the official state tree of the state of Arizona in 1954, although two distinct species were lumped together by the state as its tree: Parkinsonia microphylla and P. florida. Both trees have green trunks and stems but the blue palo verde has more of a blue-green tint. The Arizona state website continues to refer to P. florida as Cercidium foridum, an earlier genus and species name which persists in the literature. Abstract The palo verde tree, Parkinsonia spp. , is well known to residents of the desert southwest and Mexico, yet there are few studies of it in the technical literature. As a drought-resistant, woody plant, it is unique in several ways, most notably its bright green trunk, stems, and petioles where most photosynthesis is performed. Stem photosynthesis is, however, not unique to this desert plant. Other unusual features of the palo verde plant include extensive root systems, heavily cutinized epidermis and vascular bundles, sunken stoma, very small leaves (leaflets), drought-deciduous behavior, idioblasts, C4 photosynthesis, and the plentiful accumulation of storage products, oil, starch, and calcium oxalate. These features make this plant uniquely fitted to thrive in arid, desert biomes. More work is required to clearly isolate and describe such tissues as the cambium, primary and secondary phloem and xylem bundles, and the extent of internal cutinization of this unusual woody plant. We conclude that the sum of these unique features make it purposefully fitted to the biomes in which it grows.