Scientists hypothesize that the family Myrtaceae arose between 60 and 56 million years ago (Mya) during thePaleocene era. Pollen fossils have been sourced to the ancient supercontinentGondwana.[4] The breakup ofGondwana during theCretaceous period (145 to 66 Mya) geographically isolated disjunct taxa and allowed for rapid speciation; in particular, genera once considered members of the now-defunct Leptospermoideae alliance are now isolated withinOceania.[5] Generally, experts agree thatvicariance is responsible for the differentiation of Myrtaceae taxa, except in the cases ofLeptospermum species now located onNew Zealand andNew Caledonia, islands which may have been submerged at the time of lateEocene differentiation.[4]
Historically, the Myrtaceae were divided into two subfamilies. Subfamily Myrtoideae (about 75 genera) was recognized as having fleshy fruits and opposite, entire leaves. Most genera in this subfamily have one of three easily recognized types of embryos. The genera of Myrtoideae can be very difficult to distinguish in the absence of mature fruits. Myrtoideae are found worldwide in subtropical and tropical regions, with centers of diversity in the Neotropics, northeastern Australia, and Malesia. In contrast, subfamily Leptospermoideae (about 80 genera) was recognized as having dry, dehiscent fruits (capsules) and leaves arranged spirally or alternate. The Leptospermoideae are found mostly in Australasia, with a centre of diversity in Australia. Many genera in Western Australia have greatly reduced leaves and flowers typical of dryer habitats.[citation needed]
The division of the Myrtaceae into Leptospermoideae and Myrtoideae was challenged by a number of authors, including Johnson and Briggs (1984), who identified 14 tribes or clades within Myrtaceae, and found Myrtoideae to be polyphyletic.[8] Molecular studies by several groups of authors, as of 2008, have confirmed the baccate (fleshy) fruits evolved twice from capsular fruits and, as such, the two-subfamily classification does not accurately portray the phylogenetic history of the family. Thus, many workers are now using a recent analysis by Wilson et al. (2001) as a starting point for further analyses of the family. This study pronounced both Leptospermoideae and Myrtoideae invalid, but retained several smaller suballiances shown to be monophyletic through matK analysis.[9]
The generaHeteropyxis andPsiloxylon have been separated as separate families by many authors in the past as Heteropyxidaceae and Psiloxylaceae.[10][8] However, Wilsonet al.[9] included them in Myrtaceae. These two genera are presently believed to be the earliest arising and surviving lineages of Myrtaceae.
The most recent classification recognizes 17 tribes and two subfamilies, Myrtoideae and Psiloxyloideae, based on a phylogenetic analysis ofplastid DNA.[11]
Many new species are being described annually from throughout the range of Myrtaceae. Likewise, new genera are being described nearly yearly.[citation needed]
Myrtaceae is foraged by many stingless bees, especially by species such asMelipona bicolor which gather pollen from this plant family. Some Australian species such asTetragonula hockingsi andT. carbonaria are also known to collect resin from the mature seed pods ofCorymbia torelliana, resulting inmellitochory as the seeds get stuck onto thecorbiculae of the bees and sometimes are successfully disposed of by colony members that remove them. But usually, they get stuck in the hives or near hive entrances instead, hence also making it a minor nuisance for some keepers as they can take up a lot of space. Fortunately, this is only known to occur in the eastern areas ofAustralia, but could occur in other neighbouring countries where someCorymbia species are native.[14]
Weevils in the tribeCryptoplini mostly use Myrtaceae as hosts. Their larvae can develop in flower and fruit buds, or ingalls (often galls already formed by other insects).[15]
^Sytsma, Kenneth J.; Litt, Amy; Zjhra, Michelle L.; Chris Pires, J.; Nepokroeff, Molly; Conti, Elena; Walker, Jay; Wilson, Peter G. (July 2004). "Clades, Clocks, and Continents: Historical and Biogeographical Analysis of Myrtaceae, Vochysiaceae, and Relatives in the Southern Hemisphere".International Journal of Plant Sciences.165 (S4):S85 –S105.Bibcode:2004IJPlS.165S..85S.doi:10.1086/421066.ISSN1058-5893.S2CID62825431.
^Sytsma, Kenneth J. and Amy Litt. 2002. Tropical disjunctions in and among the Myrtaceae clade (Myrtaceae, Heteropyxidaceae, Psiloxylaceae, Vochysiaceae): Gondwanan vicariance or dispersal? (Abstract). Botany 2002 Conference, University of Wisconsin, Madison, Wisconsin, August 4–7, 2002.
^Wilson, P. G. (2011) Myrtaceae. In The Families and Genera of Vascular Plants. Volume X. Sapindales, Cucurbitales, Myrtaceae, edited by K. Kubitzki, X:212–71. Heidelberg: Springer-Verlag, 2011.
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