Takht. ex Reveal
The Gunnerales are an order of flowering plants. In the APG III system (2009) it contains two genera: Gunnera (in family Gunneraceae) and Myrothamnus (in family Myrothamnaceae). In the Cronquist system (1981), the Gunneraceae were in the Haloragales and Myrothamnaceae in the Hamamelidales. DNA analysis was definitive, but the grouping of the two families was a surprise, given their very dissimilar morphologies. In Cronquist's old system (1981, 1988), and Takhtajan's (1997), the Gunneraceae were in the Rosidae, and the Myrothamnaceae were in the Hamamelids. In modern classification systems such as APGIII, this order was the first to derive from the core eudicots.
The plants are dioecious, have small flowers without perianth, and the stigma is at least weakly secretory. Gunnerales characters that share with the core of the eudicots are cyanogenesis via phenylalanine, metabolic pathways of isoleucine or valine, presence of the DNA sequence of PI-dB motif, 9 and is common to suffer a small deletion in the sequence of 18S ribosomal DNA. The characters which it shares with the core of eudicotyledons, and also with Buxales and Trochodendrales are: absence of benzylisoquinoline alkaloids, euAP3 + TM6 genes (gene duplication paleoAP3: Class B), and loss of the mitochondrial gene rps2.
Despite being related, the Myrothamnaceae and the Gunneraceae look very different:
- The Gunneraceae are a mesophilic herb (often oversized), and the hydathodes are well developed and secrete mucilage or perhaps a resinous coating.
- The Myrothamnaceae are a reviviscent shrub of arid habitats, and the hydathodes are poorly developed and secrete plant resin.
Both have flowers without perianth, but the details of pollen (e.g. Zavada and Dilcher see 1986 10, Wanntorp et al. 2004th 2004b 11 and 12) differ. In Wilkinson 2000 13 is a table of differences.
- Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III" (PDF). Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. Retrieved 2013-07-06.