Monadelpha (Euphorbiaceae, Plukenetieae), a new genus of Tragiinae from the Amazon rainforest of Venezuela and Brazil.

Monadelpha L.J.Gillespie & Card.-McTeag., gen. nov., is described as a new member of Euphorbiaceae tribe Plukenetieae subtribe Tragiinae, to accommodate Tragia guayanensis, a species known from western Amazonas, Venezuela and, newly reported here, from Amazonas, Brazil. The genus is unique in the subtribe for having 5-colpate pollen and staminate flowers with filaments entirely connate into an elongate, cylindrical staminal column terminated by a tight cluster of anthers. Phylogenetic analyses based on nuclear rDNA ITS and sampling 156 accessions across the diversity of Tragiinae (all 12 genera and 77 of ~195 species) also support Monadelpha as a distinct lineage that is separate from Tragia. A revised key to the genera of Tragiinae in South America and Central America is provided.

Introduction

Members of tribe are morphologically unusual within for frequently possessing stinging hairs, twining vine or liana habit, and colorful pseudanthia (in ). The tribe is characterized by apetalous flowers, valvate staminate sepals, and undivided styles that are basally to entirely connate. contains three subtribes (i.e., , , ), of which is the largest and most diverse, with 12 genera and ~195 species as currently circumscribed (Webster 2014; with updates by Medeiros et al. 2013; Cardinal-McTeague and Gillespie 2016) (Table 1). Subtribe is distinguished from by stinging hairs and consistently 3-locular ovaries and eglandular leaves, and from by racemose or thyrsoid inflorescences rather than bibracteate pseudanthia (Gillespie 1994a; Webster 2014).

Table 1.

genera and infrageneric taxa of : species number, geographic distribution, and pollen morphology. Adapted from Cardinal-McTeague and Gillespie (2016) with pollen characters from Gillespie (1994a, 1994b) and taxonomic updates from this paper.

Genus/section	spp. #	Geographic distribution	Pollen apertures	Pollen tectum
Acidoton Sw.	5	Hispaniola, Jamaica	inaperturate	rugulate
Bia Klotzsch	5	Costa Rica to South America	inaperturate	foveolate-fossulate or finely reticulate
Cnesmone Blume	11	SE Asia	weakly 3-colpate	punctate
Ctenomeria Harv.	2	South Africa	weakly 3-aperturate	finely foveolate-reticulate
Gitara Pax & K.Hoffm.	1	Central and South America	3-colpate	finely foveolate-reticulate
Megistostigma Hook.f.	5	SE Asia	weakly 3-colpate to inaperturate	punctate
Monadelpha L.J.Gillespie & Card.-McTeag., gen. nov.	1	Venezuela (Amazonas), Brazil (Amazonas)	5-colpate	foveolate
Pachystylidium Pax & K.Hoffm.	1	SE Asia	weakly 3-porate	punctate
Platygyna P.Mercier	7	Cuba	inaperturate	reticulate or rugulate
Sphaerostylis Baill.	2	Madagascar	unknown	unknown
Tragia L.	~150	Pantropical to warm temperate
sect. Agirta Baill.	5	Madagascar	unknown	unknown
sect. Lassia (Baill.) Müll.Arg.	2	Madagascar	3-colpate	reticulate
sect. Leptobotrys (Baill.) Müll.Arg.	2	SE USA	weakly 3-porate	punctate
sect. Tagira Müll.Arg.	82	Africa, Madagascar, S Asia	3-colpate	reticulate
sect. Tragia	53	S USA to South America, Caribbean	3-colpate	intectate-baculate
Australian species group	3	Australia	3-porate	punctate
T.biflora Urb. & Ekman (unplaced)	1	Hispaniola	unknown	unknown
T.rubiginosa Huft (unplaced)	1	Venezuela	4-colpate	punctate
subg. Mauroya Leandri	1	Madagascar	weakly 3-aperturate	finely reticulate
Tragiella Pax & K.Hoffm.	4	E and S Africa	3-colpate	reticulate
Zuckertia Baill.	2	Mexico, Central America	3-colpate	finely reticulate

Among , the most species-rich genus is , which includes ~150 species, whereas the other 11 genera are much smaller with only one to 11 species each (Table 1). The complex infrageneric classification of currently comprises two subgenera, six sections (including sect. L.J.Gillespie), one species group, and two unplaced species (Table 1). A single species has been segregated as (Leandri 1971); however, our preliminary research suggests this species is closely allied with sect. and does not warrant subgeneric status. All other species belong to . Three other sections, sects. (Klotzsch) Müll.Arg., (Klotzsch) Müll.Arg. and Müll.Arg., that are sometimes considered distinct are included here within sect. , a position supported by pollen (Gillespie 1994a) and molecular studies (Cardinal-McTeague and Gillespie 2016). species exhibit very diverse pollen and floral morphology that is correlated in part with its infrageneric classification (Gillespie 1994a, b). The genus was suggested to be highly paraphyletic based on this morphological diversity (Gillespie 1994a), which is confirmed by recent molecular phylogenetic studies focused on (Cardinal-McTeague and Gillespie 2016). Three sections of , sects. (Klotzch) Müll.Arg., (Harv.) Benth., and (Baill.) Müll.Arg., were recently reinstated as genera (Webster 2007, 2014; Medeiros et al. 2013) based on inferences from pollen morphology (Gillespie 1994a), floral morphology, and preliminary molecular results (Wurdack et al. 2005), and are supported by our more in-depth molecular study (Cardinal-McTeague and Gillespie 2016).

One of the most unusual species of is L.J.Gillespie, which was considered so distinct as to merit its own monotypic section, L.J.Gillespie (Gillespie 1994b). The species is characterized by two features unique in : 5-colpate pollen and filaments entirely connate into an elongate cylindrical staminal column (Figs 1, 2). All other species have 3-aperturate pollen, which is mostly 3-colpate, sometimes 3-porate or with three poorly defined apertures (Table 1), with the exception of 4-colpate in Huft (preliminary observations in Gillespie 1994b), a species unplaced in the sectional classification. Filaments in staminate flowers of are usually distinct to sometimes basally connate. The only other species having filaments entirely connate is Radcl.-Sm. & Govaerts of sect. , which has stamens connate into a very short disc-like structure (Baillon 1858: pl. 4, figs 24, 25; pers. obs.), and very different from that of . When describing , Gillespie (1994b) suggested the species was distinct and not closely related to any other species. Nevertheless, she maintained the species within in its own section pending further study and anticipating that a major reclassification along phylogenetic lines would be necessary.

Figure 1.

Illustration of . A habit showing staminate inflorescence B staminate flower C habit showing infructescence D pistillate flower E mericarp of dehisced capsule with enclosed seed F seed, lateral view with hilum at top. Sources: A, B based on Stergios & Aymard 9182 (MO) C–F based on Stergios & Aymard 9182 (NY). Illustration by Cathy Pasquale reproduced from Gillespie (1994b) with permission from the Missouri Botanical Garden Press.

Figure 2.

Pollen morphology of A SEM of pollen grain showing polar view with five colpi B closeup of mesocolpium and two colpi. Source: Stergios & Aymard 9182 (MO). Figure reproduced from Gillespie (1994b) with permission from the Missouri Botanical Garden Press.

Here we present molecular phylogenetic results placing within subtribe that supports its recognition as a distinct genus. The new genus is described for based on its unique pollen and floral morphology and isolated phylogenetic position within . This is the first of several contributions towards a new phylogenetic classification of subtribe .

Material and methods

Molecular phylogeny

To determine the phylogenetic relationships of , we sequenced and analyzed the Internal Transcribed Spacer (ITS) region (including complete ITS1, 5.8S, and ITS2, and flanking portions of 18S and 26S) of nuclear rDNA. ITS has been shown to provide good resolution of in the prior studies (e.g., Cardinal-McTeague and Gillespie 2016; Cardinal-McTeague et al. 2019) from which our core taxon sampling is drawn and presents few alignment problems across genera. Orthologous plastid data could not be recovered from the degraded sample, but the limited phylogenetic resolution of the more slowly evolving plastid loci is established and their addition would be unlikely to change our findings. Our taxon sampling of 156 accessions included 77 of ~195 species of (39% of total diversity) with representatives of all 12 genera and seven of the eight sections/species groups in (excluding the Madagascan subg. , only known from its type collection of Leandri). Due to unusually high GC content in the close relatives of (which results in challenging DNA alignments and recovers some questionable relationships; Cardinal-McTeague, unpublished data), we rooted the tree using three accessions from the sister clade of , which contains tribes and Caryodendreae (Wurdack et al. 2005; Cervantes et al. 2016).

Extractions of genomic DNA, fluorescent Sanger sequencing, and contig assembly for the ITS sequences followed the protocols of previous molecular studies in (Cardinal-McTeague and Gillespie 2016; Cardinal-McTeague et al. 2019). The paratype of (Williams 14990, US) was sampled and sequenced at the Smithsonian separately from all other new data, under more stringent conditions for degraded museum samples following protocols in Dorr et al. (2018). That specimen is well preserved and the data appear authentic based on appropriate negative controls and unique phylogenetic placement. The sequences were aligned using the auto-select algorithm of MAFFT ver. 7.450 (Katoh and Standley 2013) in Geneious ver. 11.1.5 (BioMatters, Auckland, New Zealand), and the optimal model of nucleotide evolution was ranked by AIC (Akaike Information Criterion) using default search parameters across three substitution schemes in jModeltest2 ver. 2.1.6 on XSEDE (Darriba et al. 2012; Miller et al. 2010). Subsequent analyses were conducted on all data in the alignment and potentially ambiguous regions were few.

We estimated a phylogenetic tree using Bayesian inference with MrBayes ver. 3.2.6 on XSEDE (Ronquist et al. 2012), executing an (MC)3 analysis with two runs of 3 million generations and sampling every 1000 generations, using the optimal model of nucleotide evolution on an unpartitioned alignment (remaining parameters as default). Runs were considered converged if ESS (effective sample size) of each parameter were >500 in Tracer ver. 1.7 (Rambaut et al. 2018), and if PSRF (potential scale reduction factor) and the standard deviation of split frequencies were close to 1.0 and <0.005, respectively, as determined by the MrBayes output. A 50% majority rule consensus tree was calculated following a 25% burn-in, resulting in Bayesian posterior probability (PP) values based on posterior distribution of 4500 trees from the combined runs. For an additional estimate of branch support, we inferred maximum likelihood bootstrap percentages (MLBP) using 1000 rapid bootstrap replicates under default parameters with RAxML-HPC ver. 8 on XSEDE (Stamatakis 2014). In the Results, we interpret strong branch support as PP >0.95 and MLBP >85. Discussion of the subclades (T1–T10) follows the naming convention of Cardinal-McTeague and Gillespie (2016) with minor adjustments.

Data resources

The data underpinning the analyses reported in this paper (DNA alignment and resulting Bayesian tree) are deposited in the Dryad Data Repository at https://doi.org/10.5061/dryad.5hqbzkh4d.

Morphology

Specimens were examined at CAN and US, on loan from MO, NY, and P (herbarium acronyms following Index Herbariorum (http://sweetgum.nybg.org/science/ih/), and from other herbaria via online images in the Global Biodiversity Information Facility (GBIF.org 01 Oct 2020 Occurrence Download https://doi.org/10.15468/dl.upmgky). The key was adapted from Gillespie (1994b), modified and updated based on examination of specimens and the following references: Mulgura de Romero and Gutierrez de Sanguinetti (1989); Radcliffe-Smith (2001); Medeiros et al. (2013); Steinmann and Ramírez-Amezcua (2013); Cardinal-McTeague and Gillespie (2016); Webster (2014).

Phylogenetic results

Our 159-terminal (80 taxa) ITS dataset, including 55 new sequences, had an aligned length of 795 characters (410 variable, 353 parsimony informative [44%], 0.7% missing data), and GTR+I+G was identified as its optimal model of nucleotide evolution. Bayesian and ML analyses revealed very similar results. The 50% majority rule Bayesian topology was well resolved with most clades strongly supported by PP and MLBP (Fig. 3).

Figure 3.

Phylogenetic relationships of . Bayesian 50% majority rule consensus tree for the 159-accession (80 taxa) ITS dataset of , demonstrating the distinct phylogenetic placement of (subclade T6/9). Subclade naming system follows Cardinal-McTeague and Gillespie (2016) with minor adjustments. Branches are labeled with Bayesian posterior probabilities (PP) and maximum likelihood bootstrap percentages (MLBP). Bold branches indicate strong support (PP >0.95, MLBP >85) and coloured boxes indicate general distribution (New World = blue, Old World = yellow).

The phylogeny is divided into two major clades with strong to moderate support, the Old World clade (T1–T3) and the New World clade (T4–T10). The resolution of subclades T1–T3 was strongly supported, with subclade T1 () sister to T2 (, ) + T3 (, embedded with sects. and , and ). Subclades T4–T10 were mostly strongly supported, with the exception of the modified subclade T6/9, which includes the new genus with moderate support (PP = 0.92, MLBP = 56). The New World clade contains a small successive grade of subclades T4 () and T5 (, ) that culminates into the strongly supported Core New World clade (T6–T10). This core clade comprises a weakly supported clade (PP = 0.90, MLBP <50) with three distinctive subclades, T6/9 (, , and ) sister to T7 () + T8 (Australian , , and ), which together are sister to the large subclade T10 (). is on a long branch, moderately supported as sister to + (PP = 0.92, MLBP = 56), and well separated from and other genera.

Discussion

The phylogenetic relationships of recovered here largely agree with previous phylogenetic analyses of based on ITS and plastid psbA-trnH data (Cardinal-McTeague and Gillespie 2016). Our increased taxon sampling (77 here compared to 50 previously) improved both resolution and support, despite including only ITS data. A noteworthy difference is the revised placement of (subclade T9, formerly weakly supported as sister to , T10; Cardinal-McTeague and Gillespie 2016), which is here strongly supported as sister to (T6), with sister to both of them. is an isolated lineage, clearly distinct from New World and Old World clades of . Support for its relationship with and (subclade T6/9) is not strong, which suggests that its position on the phylogeny may not be stable and could vary with additional sequence data. Inclusion of the ITS sequence in a broader analysis of that sampled six loci (nuclear ribosomal ETS, ITS; low copy KEA1, TEB; plastid matK, ndhF; results not shown) recovered similar results with strong support for subclade T6/9, the inclusion of in subclade T6/9, and with weak support for generic relationships therein (Cardinal-McTeague et al., unpublished).

The 5-colpate pollen of is unique among . All other have 3-aperturate or inaperturate pollen, with the exception of (discussed below). Among New World , , , and pollen is 3-colpate, whereas pollen of , , and is inaperturate, and is 3-porate (Gillespie 1994a, 1994b) (Table 1). shares uneven colpus margins with the 3-colpate taxa. Its tectate-foveolate exine is more similar to the tectate and finely fossulate-reticulate or finely reticulate exines of and than to the intectate-baculate exine of .

is also morphologically distinct, especially its staminate flowers with filaments completely connate into a long cylindrical staminal column bearing a tight terminal cluster of ±5 anthers. , , , , and all have numerous free stamens, the large sects. and have 3 stamens (sometimes more, to 22) that are distinct or connate only at the base, and has two stamens (rarely 3) connate basally. Only the distantly related () of Madagascar has stamens or filaments entirely connate, but this feature has obviously evolved independently. Its androecium, consisting of a small 3-anthered disc-shaped structure on a very short narrow column, is very different from that of .

Other characters of that are unusual for include unisexual inflorescences and long, mostly distinct styles. Whereas most have bisexual inflorescences with pistillate flowers proximal, shares unisexual inflorescences with and the Caribbean genera and (plus a few species of Old World ). Styles of are slender, cylindrical, mostly smooth (papillose only at the apex), up to 10 mm long, and connate basally (up to ¼ their length). Most New World and Old World have styles that are much shorter, relatively thicker, and basally to mostly connate into a thick stylar column. Perhaps most similar is with somewhat longer (to 5 mm), slender cylindrical styles that are connate into a slender column, but differ in the degree of connation (1/2–3/4 their length) and the free portion papillose adaxially.

from Amazonian Peru is another morphologically unusual species (Huft 1989) that is unplaced in the present sectional classification. The species has 4-colpate pollen (preliminary observations in Gillespie 1994b) and is the only species in other than with a pollen aperture number greater than three. Its broad, thick, subsessile stigmas are unique in and its staminate flowers with five sessile anthers are unusual. The species is morphologically distinct from , and the two taxa are unlikely to be closely related. Molecular data is not yet available to determine its phylogenetic position within .

The isolated phylogenetic position (including a long branch length), and accompanying distinctive stamen and pollen morphology all support the recognition of as a new genus separate from . Our results suggest a possible relationship with the northern South American and Central American monotypic genus and the Mexican and Central American ditypic genus .

Taxonomic treatment

L.J.Gillespie & Card.-McTeag. gen. nov.

29001A7D-7D95-55A6-8243-163EA39A7711

urn:lsid:ipni.org:names:77213225-1

L.J.Gillespie, Novon 4: 331. 1994.

Diagnosis.

Similar to and other genera but differing in having 5-colpate pollen and monadelphous stamens with filaments entirely connate into an elongate, cylindrical staminal column with anthers tightly clustered together at apex.

Type and only known species.

(L.J.Gillespie) L.J.Gillespie & Card.-McTeag.

Description.

Habit climbing vines, apparently monoecious; latex absent; stems twining; stems, leaves and inflorescences with stinging and simple hairs. Stipules narrowly triangular or lanceolate, small, caducous. Leaves simple, alternate, evergreen, petiolate, eglandular; blades elliptic, ovate-elliptic, broadly elliptic, broadly ovate-elliptic, or suborbicular, chartaceous, apex acuminate, base narrowly cordate, margins irregularly serrulate or denticulate with minute glandular setae, venation pinnate; petiolar and laminar glands absent. Inflorescences slender racemes, unisexual, flowers single per node in bract axil; bracts small, lanceolate or narrowly lanceolate, eglandular; staminate inflorescence axillary; pistillate inflorescence (known only in fruiting stage) terminal but appearing leaf-opposed. Staminate flowers pedicellate; sepals 5, narrowly oblong, valvate; corolla and disc absent; stamens apparently 5, monadelphous; filaments connate into an elongate, ±cylindrical staminal column, bearing a dense cluster of ±5 anthers; pollen 5-colpate, oblate-spheroidal to suboblate, amb pentagonal, exine tectate-perforate, tectum foveolate and microverrucate, colpi with uneven margins. Pistillate flowers (description based on old flowers on infructescence axis) pedicellate; sepals 6, ovate, distinctly imbricate, margins entire; corolla and disc absent; ovary 3-locular with 1 ovule per locule, 3-lobed, densely covered with stinging hairs; styles 3, long-cylindrical, mostly distinct, connate basally for 10–25% length, papillose at apex. Fruits 3-lobed capsules, dehiscing into 3 bivalved mericarps; pericarp woody, sparsely covered with stinging hairs; columella persistent, with 3 perpendicular apical arms; seeds 3, subglobose, abaxial surface somewhat obtusely angular, ecarunculate; sepals persistent.

Etymology.

The genus name is combined from monos (Greek, one) and adelphos (Greek, brother), and refers to monadelphous with filaments united and to .

(L.J.Gillespie) L.J.Gillespie & Card.-McTeag. comb. nov.

30314F57-75C4-5DAA-A856-DEE5AFA155EB

urn:lsid:ipni.org:names:77213226-1

Figures 1 , 2

L.J.Gillespie, Novon 4: 330–338. 1994.

Type.

Venezuela. Amazonas: Río Casiquiare entre la boca del [Rio] Siapa y el caño Momoni, 18 Feb–4 Mar 1986, B. Stergios & G. Aymard 9182 (holotype: MO-260419! – staminate; isotype: NY-00076710! – pistillate).

See Gillespie (1994b). Emended here (based on Ule 5013): Leaves: petiole 2–8 cm long, blade elliptic, ovate-elliptic, broadly elliptic, broadly ovate-elliptic, or suborbicular, 12–25 × 6–17 cm, apex with acumen 1–2 cm long, base cordate with narrow sinus 0.8–2.5 cm deep, margins irregularly serrulate or denticulate. Staminate inflorescences ~3–18 cm long.

The specific epithet is derived from Guayana, and refers both to the Guayana Shield region of northern South America and to the Guayana Region of Venezuela where the species is native. Guayana is of Amerindian derivation by European colonists, and may come from the tribe Guayanos or the Indigenous word uayana, meaning pale (see Berry et al. 1995).

Additional collections examined.

Brazil. Amazonas: Rio Juruá, Nov 1900, E.H.G. Ule 5013 (L-0160690, K-001205092). Venezuela. Amazonas: En la isla de Trapichote, Delta del Ventuari, [], alt. 125 m, 21 Apr 1942, L. Williams 14990 (paratypes: F-1189188, US-1833601).

Distribution and preliminary conservation status.

Known from only three collections. The two from Venezuela are ~220 km apart in lowland rainforests of the upper Orinoco Basin and Río Casiquiare of western Amazonas. The Brazilian collection occurs at least 500 km to the south along the Rio Juruá (locality imprecise) in Amazonas. They occur in remote, pristine rainforest and their IUCN Red List Category presently should be Data Deficient given limited information of distribution and threats.

Notes.

is newly reported here from Brazil based on one 1900 collection by E.H.G. Ule. Staminate inflorescences on this collection (L-0160690 sheet) are considerably longer than previously described, and are closer in length to the pistillate inflorescence. It appears that the staminate inflorescence on the holotype may be damaged and partly missing or possibly less mature. Leaf blades are more variable in size and shape than on the two Venezuelan collections, some blades being very similar, others larger and relatively broader.

has unisexual inflorescences and is likely monoecious (rather than dioecious). Although unisexual inflorescences are not found on the same branch, the type collection, Stergios & Aymard 9182, has inflorescences of both sexes, and is thus monoecious if one assumes branches originate from a single individual. Further collections are needed to confirm this character.

1	Filaments absent or entirely connate into an elongate staminal column; pollen 4- or 5-colpate; inflorescences unisexual, racemose; staminate flowers with 5 sepals and 5 stamens	2
–	Filaments distinct or rarely partly connate; pollen 3-colpate, weakly 3-porate, or inaperturate; inflorescences bisexual (unisexual in Gitara), racemose or paniculate with a single branch; staminate flowers with 3–5 (6) sepals and (1) 2–40+ stamens	3
2	Anthers in a dense cluster on an elongate ±cylindrical staminal column; pollen 5-colpate; styles cylindrical, 6–10 mm long	Monadelpha
–	Anthers sessile; pollen 4-colpate; stigmas subsessile, broad	Tragiarubiginosa
3	Inflorescences unisexual; dioecious, erect shrubs; anther connective with tuft of stinging hairs	Gitara
–	Inflorescences bisexual with pistillate flowers basal; monecious vines, herbs, or subshrubs; anther connective lacking tuft of stinging hairs or present but minute	4
4	Inflorescences racemose, with 1 (2) pistillate flower(s) at the basal 1 (–9) node(s) (T.polyandra with (1) 2–4 (5) flowers on a short basal branch); stamens (1) 2–5 (–22); staminate disc usually absent, if present comprising a single central structure; pollen exine intectate, baculate	Tragia (sect. Tragia)
–	Inflorescences consisting of a racemose staminate main axis and a single elongate basal branch bearing 5–30 pistillate flowers (branch short with (1) 2–4 flowers in Zuckertiamanuelii); stamens 6–40+; staminate disc segmented or absent; pollen exine tectate, finely reticulate or foveolate-fossulate	5
5	Staminate flowers with 3 (4) sepals, 5–10 disc segments, and 6–20 stamens; leaf blades 5–16 cm long, usually unlobed; pollen inaperturate; South America to Costa Rica	Bia
–	Staminate flowers with 5 or 6 sepals, no disc, and 17–40+ stamens; leaf blades (7–) 12–25 cm long, unlobed to 3-lobed; pollen tricolpate; Mexico and Central America	Zuckertia