Recognition of the genus Thaumatophyllum Schott − formerly Philodendron subg. Meconostigma (Araceae) − based on molecular and morphological evidence

Philodendron subgenus Meconostigma has been a well-circumscribed group since 1829. Members of this group are easily distinguished by diagnostic morphological characters as well as by a distinct ecology and geographical distribution. Based on molecular, morphological and cytological evidence, we propose the recognition of P. subg. Meconostigma as a distinct genus, Thaumatophyllum Schott. We also present the necessary new combinations, an emended key and some nomenclatural and taxonomic corrections regarding 21 names of Thaumatophyllum

Large emissions from floodplain trees close the Amazon methane budget

Wetlands are the largest global source of atmospheric methane (CH4), a potent greenhouse gas. However, methane emission inventories from the Amazon floodplain, the largest natural geographic source of CH4 in the tropics, consistently underestimate the atmospheric burden of CH4 determined via remote sensing and inversion modelling, pointing to a major gap in our understanding of the contribution of these ecosystems to CH4 emissions. Here we report CH4 fluxes from the stems of 2,357 individual Amazonian floodplain trees from 13 locations across the central Amazon basin. We find that escape of soil gas through wetland trees is the dominant source of regional CH4 emissions. Methane fluxes from Amazon tree stems were up to 200 times larger than emissions reported for temperate wet forests6 and tropical peat swamp forests, representing the largest non-ebullitive wetland fluxes observed. Emissions from trees had an average stable carbon isotope value (δ13C) of −66.2 ± 6.4 per mil, consistent with a soil biogenic origin. We estimate that floodplain trees emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams of CH4 a year, in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Furthermore, we provide a ‘top-down’ regional estimate of CH4 emissions of 42.7 ± 5.6 teragrams of CH4 a year for the Amazon basin, based on regular vertical lower-troposphere CH4 profiles covering the period 2010–2013. We find close agreement between our ‘top-down’ and combined ‘bottom-up’ estimates, indicating that large CH4 emissions from trees adapted to permanent or seasonal inundation can account for the emission source that is required to close the Amazon CH4 budget. Our findings demonstrate the importance of tree stem surfaces in mediating approximately half of all wetland CH4 emissions in the Amazon floodplain, a region that represents up to one-third of the global wetland CH4 source when trees are combined with other emission sources

Floral Evolution of <i>Philodendron</i> Subgenus <i>Meconostigma</i> (Araceae)

<div><p>Elucidating the evolutionary patterns of flower and inflorescence structure is pivotal to understanding the phylogenetic relationships of Angiosperms as a whole. The inflorescence morphology and anatomy of <i>Philodendron</i> subgenus <i>Meconostigma</i>, belonging to the monocot family Araceae, has been widely studied but the evolutionary relationships of subgenus <i>Meconostigma</i> and the evolution of its flower characters have hitherto remained unclear. This study examines gynoecium evolution in subgenus <i>Meconostigma</i> in the context of an estimated molecular phylogeny for all extant species of subgenus <i>Meconostigma</i> and analysis of ancestral character reconstructions of some gynoecial structures. The phylogenetic reconstructions of all extant <i>Meconostigma</i> species were conducted under a maximum likelihood approach based on the sequences of two chloroplast (<i>trn</i>k and <i>matK</i>) and two nuclear (ETS and 18S) markers. This topology was used to reconstruct the ancestral states of seven floral characters and to elucidate their evolutionary pattern in the <i>Meconostigma</i> lineage. Our phylogeny shows that <i>Meconostigma</i> is composed of two major clades, one comprising two Amazonian species and the other all the species from the Atlantic Forest and Cerrado biomes with one Amazonian species. The common ancestor of the species of subgenus <i>Meconostigma</i> probably possessed short stylar lobes, long stylar canals, a stylar body, a vascular plexus in the gynoecium and druses in the stylar parenchyma but it is uncertain whether raphide inclusions were present in the parenchyma. The ancestral lineage also probably possessed up to 10 ovary locules. The evolution of these characters seems to have occurred independently in some lineages. We propose that the morphological and anatomical diversity observed in the gynoecial structures of subgenus <i>Meconostigma</i> is the result of an ongoing process of fusion of floral structures leading to a reduction of energy wastage and increase in stigmatic surface.</p></div

Maximum-likelihood phylogenies based on the isolated markers ETS and <i>matK</i>.

<p>a. Phylogeny based on ETS marker, b. Phylogeny based on <i>matK</i> marker. aLRT values ≥85% are indicated in the branch nodes.</p

Bayesian analysis phylogeny of <i>Meconostigma</i> species based on ETS and <i>matK</i> markers.

<p>Posterior probabilities ≥85% are indicated in the branch nodes.</p

Morphological characters of <i>Philodendron</i> subg. <i>Meconostigma</i>.

<p>a. <i>P. bipinnatifidum</i> inflorescence as an example of a typical <i>Philodendron</i> subg. <i>Meconostigma</i> inflorescence, b. Upper view of some of the <i>P. bipinnatifidum</i> female flowers showing stylar lobes, c. Longitudinal cut of <i>P. bipinnatidifum</i> female flowers, d. Transversal cut of a <i>P. bipinnatifidum</i> female flower, e. Longitudinal cut of a <i>P. adamantinum</i> female flower. Acronyms list: MZ = male zone; SZ = sterile male zone; FZ = female zone; SL = stylar lobes; SB = stylar body; SC = stylar canals; Ov = ovules; Lo = locules; Dr = druses; Ra = raphides.</p

Maximum-likelihood phylogeny of <i>Meconostigma</i> species based on ETS and <i>matK</i> markers.

<p>aLRT values ≥85% are indicated in the branch nodes.</p

Specimens of <i>Philodendron</i> subg. Meconostigma.

<p>a. A hemiepiphytic specimen of <i>P. goeldii</i> indicated by the white arrow in the Amazon Forest (Manaus city, Amazonas state), b. <i>P. goeldii</i> leaf. c. A P. corcovadense individual growing directly on sand in the Atlantic Rainforest, Restinga vegetation (Maricá city, Rio de Janeiro state), d. A hemiepiphytic specimen of <i>P. williamsii</i> in the Atlantic Rainforest <i>s.s.</i>, (Itacaré city, Bahia state), e. A population of <i>P. leal-costae</i> pointed by the white arrow in the Caatinga inselberg (Milagres city, Bahia state), f. Bromelicolous habit of <i>P. leal-costae</i>, g. <i>P. saxicola</i> rupicolous habit in the Cerrado biome, <i>campo rupestre</i> vegetation (Lençóis city, Bahia state).</p

Ancestral character reconstruction of seven morphological features of gynoecium.

<p>a. Stylar lobes size, b. Stylar canal size, c. Presence of stylar body, d. Presence of stylar vascular plexus, e. Presence of raphides in the stylar parenchyma, f. Presence of druses in style and g. Number of locules in the ovary. The colored area represents the proportional likelihood of character presence.</p