Emmotaceae van Tieghem in Bot. Jahresber. (Just) 25(2): 406. 19 Jan 1900; Emmotales Doweld, Tent. Syst. Pl. Vasc.: li. 23 Dec 2001

Distribution Tropical regions in the Old World, Mexico, Central America, the West Indies, tropical South America.

Fossils Pollen fossils attributed to Platea are known from the Paleocene of North America and Greenland.

Habit Usually bisexual (Platea dioecious), evergreen trees, shrubs or lianas.

Vegetative anatomy Phellogen ab initio superficial? Secondary lateral growth in Rhaphiostylis anomalous via successive (concentric) cambia. Vessel elements with simple (Rhaphiostylis) or scalariform (rarely reticulate) perforation plates; lateral pits usually scalariform to opposite (sometimes alternate), bordered or (in at least Poraqueiba and Metteniusa) simple pits. Imperforate tracheary xylem elements tracheids (or fibre-tracheids?) with bordered pits, non-septate. Wood rays uniseriate or multiseriate, homocellular or heterocellular. Axial parenchyma apotracheal usually diffuse-in-aggregates (rarely diffuse), or paratracheal scanty or banded. Tyloses usually absent (sclerotic sometimes abundant). Sieve tube plastids S type? Nodes 1:1, unilacunar with one leaf trace, or 3:3, trilacunar with three traces (in Metteniusa 5:5, pentalacunar with five leaf traces, at petiole base in a U-shaped configuration, distally separate). Heartwood often with gum-like substances. Prismatic calciumoxalate crystals abundant (rhombic crystals abundant in Rhaphiostylis); druses frequent in flowers; styloid-like crystals and crystal groups present in wood ray cells of Apodytes.

Trichomes Hairs unicellular, unbranched, T-shaped, or absent (in Platea glandular and stellate-peltate or lepidote, sometimes caducous or absent).

Leaves Alternate (spiral or distichous), simple, entire, in Platea with conduplicate ptyxis. Stipules and leaf sheath absent. Petiole vascular bundle transection arcuate, complex (Metteniusa). Venation pinnate, brochidodromous or eucamptodromous. Stomata anomocytic or cyclocytic (anomocyclocytic). Cuticular wax crystalloids? Mesophyll with fibres. Domatia absent. Leaf margin serrate to entire.

Inflorescence Terminal (Apodytes) or axillary, panicle, cymose, cymose thyrsoid, fasciculate to corymbose cyme, or compound or simple racemes. Floral prophylls (bracteoles) (two or) three per flower, thick, triangular.

Flowers Actinomorphic, small to large. Pedicel articulated. Hypogyny. Sepals four or five, with imbricate quincuncial to imbricate aestivation, persistent, connate. Petals four or five, with valvate aestivation, free or connate at base (in Metteniusa late sympetaly, i.e. in late stage connate in lower part; petals absent in female flowers of Platea), sometimes with adaxial hairs. Nectary absent. Disc absent. Secretory hairs present.

Androecium Stamens four or five, haplostemonous, antesepalous, alternipetalous. Filaments long, subulate, free from each other, free from or adnate (at least at base) to corolla tube (epipetalous). Anthers basifixed to dorsifixed, versatile, usually tetrasporangiate (in Metteniusa polysporangiate; in Emmotum disporangiate, monothecal), septate, latrorse to extrorse or introrse, longicidal (dehiscing by longitudinal slits, in Metteniusa long and moniliform, with 17 or fewer partial microsporangia – locelli – in four vertical rows opening individually); thecae in Metteniusa strongly recurved following dehiscence; connective often enlarged (in Metteniusa massive). Tapetum secretory. Staminodia absent.

Pollen grains Microsporogenesis simultaneous? Pollen grains tricolporate, shed as monads, bicellular at dispersal? Exine scabrate (Metteniusa) or semitectate, with columellate? infratectum, foveate-reticulate (Apodytes), with ? infratectum, sculpturing?

Gynoecium Pistil composed of usually three (in Metteniusa five paracarpous) connate carpels, with a single fertile carpel, leading to pseudomonomery (one carpel in Apodytes modified into fleshy dispersal structure; in Emmotum three fertile and two sterile carpels); carpel initials congenitally fused by their margins; gynoecium zygomorphic throughout ontogeny (indicating pseudomonomery). Ovary superior, usually unilocular due to pseudomonomery (in Emmotum bilocular or trilocular, pseudotrimerous), with or without a fleshy appendage. Style single, simple, long, narrow (in Metteniusa filiform), often short. Stigma subcapitate, capitate, punctate, discoid, bilobate or slightly trifid, slightly papillate, type? Pistillodium absent.

Ovules Placentation apical, subapical to axile (pseudoparietal), collateral or superposed (in Metteniusa parietal). Ovules two per fertile carpel or two per ovary (in Metteniusa one ovule primordium developing in each of two smaller carpels), orthotropous, pendulous, bitegmic (Emmotum) or unitegmic, crassinucellar, anatropous, pendulous, unitegmic, tenuinucellar, three larger carpels (including median carpel) sterile. Integument in Metteniusa more than 20 cell layers thick, massive, highly vascularized. Megagametophyte monosporous, Polygonum type? Endosperm development? Endosperm haustoria? Embryogenesis?

Fruit A usually one-seeded drupe (with one ovule aborted), often flattened. Pyrene usually asymmetrical, often with ribs or ridges (in Metteniusa asymmetrically arranged) and persistent lateral-basal style.

Seeds Aril absent. Funicle massive and elongated. Testa membranous, vascularized. Exotestal cells? Endotesta? Tanniniferous cells abundant. Perisperm not developed. Endosperm copious, oily? Embryo usually straight (in Metteniusa curved), short to long, well differentiated, with chlorophyll? Cotyledons two, foliaceous. Germination?

Phytochemistry Route I iridoids (e.g. daphylloside), monoterpene secoiridoids and emmotins (eudesmane sesquiterpenes), oleanolic acid. Cyanogenic compounds? Tannins present. Aluminium accumulated in Platea.

Systematics Plateoideae G. W. Stull in Amer. J. Bot. 102: 1809. Nov 2015. Platea (5; P. bullata, P. excelsa, P. latifolia, P. parvifolia, P. sclerophylla; Indochina, Malesia to New Guinea), Calatola (5; C. costaricensis, C. laevigata, C. mollis, C. sanguininensis, C. uxpanapensis; Mexico to Ecuador). – Apodytoideae G. W. Stull in Amer. J. Bot. 102: 1809. Nov 2015. Apodytes (8; tropical and subtropical regions of eastern and southern Africa, Madagascar, southern India, Sri Lanka, Mauritius, Indochina, Malesia to New Guinea, Queensland, New Caledonia), Rhaphiostylis (11; tropical West Africa), Dendrobangia (2; D. boliviana, D. multinervia; Costa Rica, tropical South America). – Metteniusoideae G. W. Stull in Amer. J. Bot. 102: 1809. Nov 2015. Emmotum (12; tropical South America), Poraqueiba (3; P. guianensis, P. paraensis, P. sericea; tropical South America); Oecopetalum (3; O. greenmanii, O. guatemalense, O. mexicanum; Mexico, Central America), Pittosporopsis (1; P. kerrii; Southeast Asia), Metteniusa (7; M. cogolloi, M. cundinamarcensis, M. edulis, M. huilensis, M. nucifera, M. santanderensis, M. tessmanniana; Costa Rica, Panamá, the northern Andes to Peru and western Venezuela), Ottoschulzia (4; O. cubensis, O. domingensis, O. pallida, O. rhodoxylon; Guatemala, the West Indies).

Calatola has vessel elements with scalariform perforation plates, nodes 3:3, trilacunar with three leaf traces, leaves with conduplicate ptyxis and serrate leaf margin.

Rhaphiostylis is very similar to Icacinaceae in its anatomy, with the exception of the banded parenchyma present in Icacinaceae.

Dendrobangia has solitary vessels with scalariform perforation plates with numerous bars and the lateral (intervessel) pits are opposite. The fibres have distinctly bordered pits. The axial parenchyma is usually diffuse-in-aggregates and scanty paratracheal. The axial parenchyma cells are chambered and contain prismatic crystals. Uniseriate and 8-seriate rays are present and the body cells are procumbent and square with few small prismatic crystals and small styloids. The leaves have lepidote-stellate hairs, brochidodromous leaf venation and cyclocytic stomata. The inflorescence is an axillary panicle. The bracteoles are two to six. The five sepals are imbricate and the five petals are basally fused into a tube and each lobe has a strap-like, apically broadened acumen. The five stamens are adnate to the corolla tube and alternate to the lobes. The anthers are basifixed. The ovary is unilocular and uniovulate. The fruit is a one-seeded drupe. The embryo is minute with a copious endosperm.

Metteniusa forms a weakly supported clade together with [Oecopetalum+Ottoschulzia] in analyses by Byng & al. (2014). Emmotum and Ottoschulzia possess vessel elements with scalariform perforation plates with less than eleven cross-ribs.

Emmotum is somewhat similar to Oncotheca (Oncothecaceae) in its monosporangiate thecae and in the gynoecium having both fertile and sterile carpels.

Cladogram of Metteniusaceae based on DNA sequence data (Stull & al. 2015).

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METTENIUSIIDAE W. Stull, D. E. Soltis et P. S. Soltis

METTENIUSALES Takht.

METTENIUSACEAE H. Karst. ex Schnizl.