A Reappraisal of Phylogentic Relationships in the Monocotyledon Family Hydrocharitaceae (Alismatidae)

Abstract

The diverse, aquatic Hydrocharitaceae have defied stable classification for nearly two centuries. Anatomical and morphological convergence characterize many aquatic plants and undoubtedly have hindered the ability of researchers to ascertain accurately those features representing reliable phylogenetic markers within Hydrocharitaceae. Most prior classifications of the family have emphasized few characters to define major taxonomic subdivisions (i.e., they were highly artificial). Previous studies using molecular data have shown that DNA sequences provide novel indications of phylogeny not indicated previously by morphologically based classifications; however, they have not yet recommended alterations to the classification for the family. We conducted a more comprehensive phylogenetic study of Hydrocharitaceae to better elucidate evolutionary relationships among the genera that in turn could be used to provide insight for improvements in classification. We analyzed different data sets (55 morphological characters; chloroplast rbcL, matK, trnK intron sequences; nuclear ribosomal ITS region sequences) singly and in various combinations using maximum parsimony and maximum likelihood methods of phylogenetic reconstruction. Phylogenetic analysis of combined data yielded a fully resolved tree depicting four well-supported, major clades within Hydrocharitaceae. We use these results to propose a phylogenetic classification of Hydrocharitaceae recognizing four subfamilies that correspond to these clades: Anacharidoideae, Hydrilloideae, Hydrocharitoideae, and Stratioideae. Phylogenetic analysis also indicated the pattern of derivation with respect to submersed lifeforms, hydrophilous pollination, and marine habitation in the family. Character reconstructions indicated that several features, (e.g., ovule type; occurrence of detaching male flowers), once thought to provide strong phylogenetic markers in Hydrocharitaceae, actually are highly homoplasious and have acutely mislead past attempts at classification of the family.

The ecology of Egeria densa Planchón (Liliopsida: Alismatales): A wetland ecosystem engineer?

“…Nine of the seventeen genera occur in South America, mostly in tropical and subtropical climates (Koehler & Bove 2001). The Hydrocharitaceae is often divided into three sub-families, but a recent molecular phylogenetic analysis indicates that there are four major sub-families (Les et al 2006). Divisions within the Hydrocharitaceae indicate that traits such as submerged lifeforms, hydrophilous pollination and marine habitation are derived relative to the basal genera in the family and a closely related outgroup (Les et al 2006).…”

“…The Hydrocharitaceae is often divided into three sub-families, but a recent molecular phylogenetic analysis indicates that there are four major sub-families (Les et al 2006). Divisions within the Hydrocharitaceae indicate that traits such as submerged lifeforms, hydrophilous pollination and marine habitation are derived relative to the basal genera in the family and a closely related outgroup (Les et al 2006). Two lifeforms are common within the family: those having a creeping monopodial rhizome with leaves arranged in two vertical rows and a more erect lifeform with basal roots and whorled or spiral leaf arrangements.…”

Flora das cangas da Serra dos Carajás, Pará, Brasil: Hydrocharitaceae

“…Assim, no presente estudo, optamos por seguir a circunscrição adotada na Flora do Brasil (BFG 2015). A família é constituída por ervas aquáticas, monoicas ou dioicas, dulciaquícolas ou marinhas, anuais ou perenes; com inflorescências subtendidas por duas brácteas normalmente conatas (espatas), com flores entomófilas, anemófilas ou hidrófilas, de ovário ínfero e estigmas geralmente divididos (Stevens 2001; Les et al 2006). No Brasil ocorrem 14 espécies distribuídas em seis gêneros (BFG 2015), dos quais dois foram registrados nas cangas da Serra dos Carajás: Ottelia Pers.…”

“…Filogenias morfológicas e moleculares mostram Apalanthe como grupo irmão do clado formado por Elodea e Egeria Planch. (e.g., Les et al 2006;Li & Zhou 2009;Ross et al 2016). Assim, combinar A. granatensis em Elodea, como tratado por alguns autores (e.g., St.…”

Flora do Rio de Janeiro: Hydrocharitaceae

“…Apesar de St. Jonh (1963) considerar Apalanthe subgênero do gênero Elodea, estudos de revisão taxonômica e filogenia confirmam a distinção destes gêneros (Cook 1985;Les et al 2006;Les & Tippery 2013 …”