Heliocaminiform structures: plant organs that function as microgreenhouses

Abstract

Plant structures that enclose trapped air are morphologically and taxonomically diverse. They range from pubescence (trichomes) on various parts of plants to flowers, inflorescences, stems, culms (above-ground jointed stems of grasses), petioles, peduncles, scapes, fruits, bracts, leaves, galls, algal pneumatocysts, moss sporophytes, lichen podetia, and fungal fruiting bodies. Despite being familiar, such structures have not been studied systematically until recently when their complex thermodynamic functionality as microgreenhouses has been recognized. We propose the term “heliocaminiform” (Greco-Latin origin for “sun-room”) provides an umbrella term that describes form and function. Almost all the hollow structures we have examined have elevated internal temperatures of several degrees C above the surrounding air in sunshine, but those are abolished under cloud or at night. The potential importance for the additional heat is presumed to be in growth, maturation, reproduction, sexual function, and overall fitness of the plants. There seem to be no experimental studies on those effects even though they may help explain aspects of plants’ responses to climate change and to phenological mismatches with symbionts (mutualists and herbivores) as ecologically co-dependent partners. Our review and observations opens a remarkably new and hitherto surprisingly neglected avenue in botany which we hope others will explore.