Rhynchostegium is a genus of pleurocarpous mosses belonging to the family Brachytheciaceae. The genus has a cosmopolitan distribution across different climatological regions except the polar regions, mostly in tropic to north temperate regions. The genus contains both aquatic and terrestrial species. The genus was named for their rostrate opercula. The type species of this genus is Rhynchostegium confertum (Dicks.) Schimp.
Etymology The genus name comes from the Greek rhyncho- (beaked) and stegos (a lid), which refers to the rostrate operculum of the sporophyte.
History The genus was first described by Bruch and Wilhelm Philippe Schimper in 1852.
Habitats Terrestrial species of Rhynchostegium live in moist to wet or shaded habitats, on rock, soil, tree base, tree stem, and logs.
Aquatic species live by or in running water, including streams, springs, rivers, beds of waterfalls, and seepy cliffs.
Morphology
Gametophyte
Rhynchostegium are small to large mosses that form either loose tuft or extensive mats on the substrate, with irregular or regular branching. The younger plants are generally deep green or light green; aging plants could become whitish, brownish, or paler green. Stems are creeping and lack hyaloderm, with acute to acuminate pseudoparaphyllia. Stem leaves are erectopatent or erect. Branch leaves are similar in morphology to stem leaves but smaller and sometimes narrower. Leaves are commonly straightly to homomallously arranged; subimbricate, subcomplanate, or complanate arrangement are sometimes seen, especially in branch leaves. Leaf base, decurrent or not, varies from ovate to ovate-cordate, occasionally lanceolate, and the narrowing from gradual to abrupt, towards a short- or long-acuminate apex, where sometimes a differentiated long acumen or apiculus is present. The leaves have a single costa that generally smoothly ends 35-75% up the leaf, and more often in branch leaves in an abaxial spine. Leaf surfaces vary from flat to slightly concave and not to strongly longitudinally plicate, with little to some pores and linear laminal cells. Leaf margins are serrate to serrulate. Axillary hairs constitute of 3-7 cells, with 1-3 upper cells. Alar cells are slightly enlarged, and either undifferentiated or quadrate to elongate-rectangular.
Sporophyte Rhynchostegium are autoicous. Covered by a naked calyptra is a rostrate to long-rostrate operculum attached to a red-brown to brown, oblong-cylindric, weakly curved capsule, which is inclined or horizontal to a red-brown, smooth seta that has abruptly contracted perichaetial leaves at the base, with acumen straight to reflexed. An annulus separates the operculum. The peristome is xerochastic and perfect, which the red to orange-red exostomes have reduced trabeculae and cross-striolae at the base of the teeth; in rare cases the exostomes are narrow and yellow. The broadly or narrowly perforated endostomes and developed to vestigial cilia are supported by a low or high basal membrane. Spore diameters range between 9-16 μm.
Biochemistry
Allelopathy
Allelopathy has been studied on Rhynchostegium pallidifolium, which usually form pure colonies in their natural habitat. Methanol extract of R.pallidifolium represses the seedling of cress, alfalfa, lettuce, ryegrass, timothy, and Digitaria sanguinalis in a concentration-dependent manner. A combination of ESI-MS and 1H NMR analyses identified the inhibitory chemical as 3-hydroxy-β-ionone. Further study showed a minimal 3-hydroxy-β-ionone concentration of 1 μM for the inhibition of cress hypocotyl growth, and 3 μM for cress root growth, while the endogenous concentration. The presence of 3-hydroxy-β-ionone in their natural substrate and the growing medium suggested secretion to the environment, which may imply an important role of 3-hydroxy-β-ionone in competition with other plants and the forming of pure colonies.
Antibacterial
Acetone extract of Rhynchostegium riparioides showed antibiotic activity on some Gram-negative bacteria, including Escherichia coli, Proteus mirabilis, Entero-bacter cloacae and Pseudomonas aeruginosa.
Ethanolic extract of Rhynchostegium vagans showed similar effect on some Gram-negative bacteria and fungi, with performance superior to chloramphenicol and fluconazole.
Applications
Freshwater monitoring Rhynchostegium riparioides is used in monitoring of heavy metals concentration in freshwater in multiple regions around the world, such as copper, zinc. R. riparioides as a neutrophilous species has been used in monitoring water acidification.
List of species The World Flora Online lists 221 species of Rhynchostegium.
Rhynchostegium acanthophyllum (Mont.) A. Jaeger Rhynchostegium acicula (Broth.) Broth. Rhynchostegium acutifolium (Hook. f. & Wilson) A. Jaeger Rhynchostegium alboviridum R.S. Williams Rhynchostegium algirianum (Brid. ex P. Beauv.) Lindb. Rhynchostegium alopecuroides (Brid.) A.J.E. Sm. Rhynchostegium altisetum Müll. Hal. Rhynchostegium ambiguum (Schwägr.) W.R. Buck Rhynchostegium anceps (Bosch & Sande Lac.) A. Jaeger Rhynchostegium aneuron Kindb. Rhynchostegium angustifolium Renauld & Cardot Rhynchostegium apophysatum (Hornsch.) A. Jaeger Rhynchostegium aquaticum A. Jaeger Rhynchostegium arcticum (I. Hagen) Ignatov & Huttunen Rhynchostegium asperisetum (Müll. Hal.) A. Jaeger Rhynchostegium assumptionis Besch. Rhynchostegium bello-intricatum (Broth.) Paris Rhynchostegium bequaertii Thér. & Naveau Rhynchostegium berteroanum (Mont.) A. Jaeger Rhynchostegium beskeanum (Müll. Hal.) A. Jaeger Rhynchostegium bifariellum (Kindb.) Kindb. Rhynchostegium brachypterum (Hornsch.) A. Jaeger Rhynchostegium brachypyxis Renauld & Cardot Rhynchostegium brachythecioides Dixon & P. de la Varde Rhynchostegium brandegei (Austin) Renauld & Cardot Rhynchostegium brevicuspis Müll. Hal. Rhynchostegium brevinerve Huttunen & Ignatov Rhynchostegium brevirete Broth. Rhynchostegium buluense (Broth.) Paris Rhynchostegium cacticola (Müll. Hal.) Paris Rhynchostegium calderi Vohra Rhynchostegium caloosiense (Austin) Renauld & Cardot Rhynchostegium campylocarpum (Müll. Hal.) De Not. Rhynchostegium campylocladulum Müll. Hal. Rhynchostegium cataractarum Thér. & P. de la Varde Rhynchostegium celebicum (Sande Lac.) A. Jaeger Rhynchostegium chrysophylloides A. Jaeger Rhynchostegium circinatum (Brid.) De Not. Rhynchostegium cirrosum (Schwägr.) De Not. Rhynchostegium collatum (Hook. & Wilson) Broth. & Watts Rhynchostegium comorae (Müll. Hal.) A. Jaeger Rhynchostegium complanum (Mitt.) A. Jaeger Rhynchostegium compridense (Müll. Hal. ex Broth.) Paris Rhynchostegium conchophyllum (Taylor) A. Jaeger Rhynchostegium confertum (Dicks.) Schimp. Rhynchostegium confusum Cezón, J. Muñoz, Hedenäs & Huttunen Rhynchostegium congruens (Hampe) Mitt. Rhynchostegium conostomus (Mont.) Huttunen & Ignatov Rhynchostegium contortulum Tixier Rhynchostegium contractum Cardot Rhynchostegium crassinervium (Taylor) De Not. Rhynchostegium cylindritheca Dixon Rhynchostegium dasyphyllum Müll. Hal. Rhynchostegium delicatulum James Rhynchostegium demissum (Wilson) Schimp. Rhynchostegium dentiferum (Hampe) A. Jaeger Rhynchostegium deplanatum (Bruch & Schimp. ex Sull.) Kindb. Rhynchostegium depressum (Brid.) Schimp. Rhynchostegium distans Besch. Rhynchostegium distratum (Hampe) A. Jaeger Rhynchostegium drepanocladioides (Müll. Hal.) Kindb. Rhynchostegium duthiei Müll. Hal. ex Dixon Rhynchostegium elusum (Mitt.) A. Jaeger Rhynchostegium erythropodium (Hampe) Mitt. Rhynchostegium esquirolii Cardot & Thér. Rhynchostegium exiguum (Blandow) Brockm. Rhynchostegium exilissimum (Sull.) A. Jaeger Rhynchostegium fabroniadelphus (Müll. Hal.) A. Jaeger Rhynchostegium fauriei Cardot Rhynchostegium finitimum (Hampe) Ångström Rhynchostegium fissidens (Müll. Hal.) Kindb. Rhynchostegium fissidentellum Besch. Rhynchostegium fragilicuspis Dixon Rhynchostegium fuegianum (Cardot) Huttunen & Ignatov Rhynchostegium funckii (Schimp.) De Not. Rhynchostegium gaudichaudii (Mont.) A. Jaeger Rhynchostegium georgianum Dixon & Grout Rhynchostegium glaucovirescens (Müll. Hal.) Kindb. Rhynchostegium globipyxis (Müll. Hal.) Kindb. Rhynchostegium gracilipes Thér. Rhynchostegium graminicolor (Brid.) A.L. Andrews Rhynchostegium herbaceum (Mitt.) A. Jaeger Rhynchostegium hians (Hedw.) Delogne Rhynchostegium homaliocaulon (Müll. Hal.) Kindb. Rhynchostegium hookeri A. Jaeger Rhynchostegium hopfferi (Welw. & Duby) A. Gepp Rhynchostegium horridum Broth. Rhynchostegium huitomalconum (Müll. Hal.) Besch. Rhynchostegium humillimum (Mitt.) A. Jaeger Rhynchostegium hunanense Ignatov & Huttunen Rhynchostegium huttonii (Hampe ex Beckett) Paris Rhynchostegium illecebrum (Schimp.) Delogne Rhynchostegium inaequale Dixon Rhynchostegium inclinatum (Mitt.) A. Jaeger Rhynchostegium inerme (Mitt.) A. Jaeger Rhynchostegium irriguum Dixon Rhynchostegium isopterygioides Cardot Rhynchostegium jamesii Sull. Rhynchostegium javanicum (Bél.) Besch. Rhynchostegium jovet-astiae Bizot Rhynchostegium laevisetum (Geh.) Mitt. Rhynchostegium lamasicum (Spruce ex Mitt.) Besch. Rhynchostegium laxatum (Mitt.) Paris Rhynchostegium laxirete Broth. Rhynchostegium leptoblastum (Müll. Hal.) Kindb. Rhynchostegium leptomerocarpum (Müll. Hal.) Besch. Rhynchostegium leptopteridium Müll. Hal. Rhynchostegium leucodictyon Müll. Hal. Rhynchostegium lindmanii (Broth.) Paris Rhynchostegium lusitanicum (Kindb.) Broth. Rhynchostegium luteonitens (Welw. & Duby) A. Jaeger Rhynchostegium mac-owanianum Paris Rhynchostegium malmei (Broth.) Paris Rhynchostegium megapolitanum (Blandow ex F. Weber & D. Mohr) Schimp. Rhynchostegium membranaceum (Müll. Hal.) Broth. Rhynchostegium menadense (Sande Lac.) A. Jaeger Rhynchostegium meridionale (Schimp.) De Not. Rhynchostegium micans (Sw.) Austin Rhynchostegium microthamnioides Müll. Hal. Rhynchostegium minutum Müll. Hal. Rhynchostegium muelleri A. Jaeger Rhynchostegium murale (Hedw.) Schimp. Rhynchostegium muriculatum (Hook. f. & Wilson) Reichardt Rhynchostegium mutatum (Ochyra & Vanderp.) Huttunen & Ignatov Rhynchostegium myosuroides (Brid.) De Not. Rhynchostegium nanopennatum (Broth.) Kindb. Rhynchostegium nanothecium Müll. Hal. ex Dixon Rhynchostegium nervosum (Kiaer ex Renauld) Broth. ex Cardot Rhynchostegium nigrescens Besch. Rhynchostegium oblongifolium Broth. & Watts Rhynchostegium obtusatum Broth. Rhynchostegium obtusifolium (Mitt.) A. Jaeger Rhynchostegium occultum Larraín, Huttunen, Ignatova & Ignatov Rhynchostegium omocrates W.R. Buck Rhynchostegium ovalfolium S. Okamura Rhynchostegium oxyodon (Welw. & Duby) A. Gepp Rhynchostegium pallidifolium (Mitt.) A. Jaeger Rhynchostegium pallidius (Hampe) A. Jaeger Rhynchostegium pampae (Müll. Hal.) Kindb. Rhynchostegium parvulum Broth. Rhynchostegium patulifolium Cardot & Thér. Rhynchostegium patulum A. Jaeger Rhynchostegium pectinatum (Mitt.) Paris Rhynchostegium pellucidum Dixon Rhynchostegium pendulum (Brid.) A. Jaeger Rhynchostegium peruviense (R.S. Williams) Ochyra Rhynchostegium pervilleanum (Schimp.) A. Jaeger Rhynchostegium philippinense (Duby) A. Jaeger Rhynchostegium piliferum (Hedw.) De Not. Rhynchostegium pinnicaule (Müll. Hal.) Kindb. Rhynchostegium plagiotheciella Müll. Hal. Rhynchostegium planifolium Müll. Hal. Rhynchostegium planiusculum (Mitt.) A. Jaeger Rhynchostegium praecox (Hedw.) De Not. Rhynchostegium praelongum (Hedw.) De Not. Rhynchostegium pringlei Cardot Rhynchostegium pseudoconfertum (Müll. Hal.) A. Jaeger Rhynchostegium pseudodistans Cardot Rhynchostegium pseudomurale (Hampe) A. Jaeger Rhynchostegium pseudoserrulatum (Kindb.) Kindb. Rhynchostegium psilopodium Ignatov & Huttunen Rhynchostegium pulchellum (Hedw.) H. Rob. Rhynchostegium pumilum (Wilson) De Not. Rhynchostegium raphidorrhynchum (Müll. Hal.) A. Jaeger Rhynchostegium recurvans (Michx.) Besch.