Liliopsida Batsch, Tab. Regni Veg.: 121. 2 Mai 1802
[Acorus+[Alismatales+[Petrosaviaceae+[Taccales+Pandanales]+[Liliales+[Iridales+ Commelinidae]]]]]
Acorineae Link, Handbuch 1: 114. 4-11 Jul 1829 [’Acoroideae’]; Acorales Link in C. F. P. von Martius, Consp. Regn. Veg.: 6. Sep-Oct 1835 [‘Acorinae’]; Acoranae Reveal in Phytologia 82: 129. 28 Nov 1997
Genera/species 1/2
Distribution Temperate and subtropical regions in Eurasia, eastern North America, southern, eastern and southeastern Asia.
Fossils There are few unambiguous fossils of Acoraceae. Some Late Barremian to Early Aptian pollen grains from Portugal may be closely allied to Acorus. Remnants of Acorus are known from the Cenozoic of North America.
Habit Bisexual, perennial herbs. Aquatic plants or hygrophytes. Aromatic.
Vegetative anatomy Root cortex with schizogenous intercellular spaces and idioblasts with ethereal oils, etc. Root stele pentarch. Phellogen absent. Stem endodermis with casparian strips. Vascular bundles amphivasal. Vessel elements in roots and rhizome, aberrant and tracheid-like, with scalariform perforation plates with pit membranes; lateral pits scalariform or transitional, simple pits. Imperforate tracheary xylem elements tracheids with simple pits. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type. Nodes multilacunar, with several leaf traces. Laticifers absent. Silica bodies absent. Calciumoxalate as druses, prismatic crystals, etc. (raphides absent).
Trichomes Hairs unicellular.
Leaves Alternate (distichous), simple, entire, isobifacial, ensiform, with ? ptyxis. Pseudolamina developing from leaf base zone or from upper part of foliar primordium. Stipules absent; leaf sheath open. Petiole vascular bundle transection? Leaf axils with intravaginal scales/colleters (squamulae intravaginales). Venation parallel. Stomata paracytic. Cuticular wax crystalloids? Mesophyll with idioblasts containing ethereal oils. Leaf margin entire.
Inflorescence Terminal, persistent fleshy spadix in axil of foliaceous green bract, spatha, seemingly forming continuation of peduncle. Peduncle foliaceous, ensiform, with two separate vascular bundle systems. Bracts and foliar prophylls (bracteoles) absent.
Flowers Slightly zygomorphic. Hypogyny. Tepals 3+3, sepaloid, persistent, free; abaxial (median) tepal in outer perianth whorl larger, resembling bract (possibly bract, then abaxial outer tepal absent; alternatively tepal strongly adnate to bract) and enclosing bud; bract and abaxial (median) outer tepal developmentally similar. Nectary probably absent. Disc absent.
Androecium Stamens 3+3, whorled. Filaments linear, free from each other and from tepals. Anthers basifixed, non-versatile, tetrasporangiate, introrse-latrorse, longicidal (dehiscing by longitudinal slits). Tapetum secretory, with binucleate to quadrinucleate cells. Staminodia absent.
Pollen grains Microsporogenesis successive. Pollen grains monosulcate to subulcerate, shed as monads, bicellular at dispersal. Exine tectate, with columellate? infratectum, foveolate to psilate; endexine lamellate.
Gynoecium Pistil composed of two or three connate carpels; carpel ascidiate and plicate (intermediate), postgenitally fused, with secretory canal (filled by secretions). Ovary superior, bilocular or trilocular; ovules enclosed by mucilage secreted from mucilaginous hairs on inner side of ovary; septa with non-secreting slits (septal nectaries?). Style single, simple, very short, wide, massive; stylar canal with mucilaginous exudate. Stigma very small, type? Pistillodium absent.
Ovules Placentation apical(-axile). Ovules two to four (or five) per carpel, orthotropous, pendulous, bitegmic, pseudocrassinucellar. Micropyle endostomal. Outer integument three or four cell layers thick. Inner integument two cell layers thick. Integuments (especially outer integument) hairy. Hypostase massive, with central columella and radiating cells. Parietal cell not formed. Nucellar cap two cell layers thick, formed by periclinal cell divisions of megasporangial epidermis. Megagametophyte monosporous, Polygonum type. Antipodal cells persistent and somewhat proliferating (up to five cells). Chalazal basal apparatus absent. Endosperm development ab initio cellular, with first division transverse and divisions uniform within endosperm halves. Endosperm haustoria absent. Embryogenesis?
Fruit A one- or several-seeded baccate fleshy capsule (more or less dehiscent) with persistent tepals.
Seeds Aril absent. Testa in Acorus gramineus with bristle-like hairs. Exotesta? Mesotesta and endotesta unspecialized. Exotegmen fibrous to sclerotic. Endotegmen? Perisperm consisting of one cell layer, oily and proteinaceous, without starch, dermal (developing from megasporangial epidermis). Endosperm copious. Embryo small, axile, cylindrical, with chlorophyll. Cotyledon one, subulate, unifacial, with distal part in the form of haustorium. Germination phanerocotylar. Radicula ephemeral. Root collar with long, densely spaced rhizoids. First leaf terete.
Cytology n = 9, 11, 12, 18, 22, 24 – Polyploidy occurring.
DNA Deletion of 3 bp in atpA. Mitochondrial intron processing according to cis-splicing mechanism.
Phytochemistry Polyphenols, ethereal oils containing phenylpropanoids, monoterpenes and sesquiterpenes, tannins, proanthocyanidins, acorine (diterpene alkaloid), and asarone present.
Use Ornamental plants, aquarium plants (Acorus gramineus), medicinal plans, perfumes, aroma for liqueurs.
Systematics Acorus (2; A. calamus, A. gramineus; temperate and subtropical regions in Eurasia, eastern North America, southern, eastern and southeastern Asia to Sulawesi and New Guinea; naturalized over large areas).
Acorus has often been hypothesized as sister-group to all other monocotyledons (Liliidae). However, it was sister, with relatively low support, to the core Alismatales (Alismatales except Tofieldiaceae and Araceae) in the analyses by Petersen et al. (2016) using molecular and morphological characters.
The leaves have possibly developed from the upper part of the leaf primordium (cf. Alismatales).
The development of the endosperm in Acorus has been much debated during the years. The development is unique among monocots, according to Holloway & Friedman (2008), in being cellular. On the other hand, Tobe & Kadokawa (2010) reinterpret the endosperm in Alismatales and Petrosaviaceae as cellular instead of helobial. The cellular development is a plesiomorphy in Liliidae, and, provided Tobe & Kadokawa (2010) are correct, nuclear endosperm has evolved two or three times in the monocotyledons: once in Alismatales, once in Petrosavia (Petrosaviaceae) and once in the ancestor of all other (‘post-petrosavian’) monocots.
The presence of the volatile toxic ether asarone in both Acorus and Asaraceae is worth notifying, although it appears to be a parallelism.
Literature
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