The Biology of the Facultative Halophyte Atriplex patula L. Volume 56- Issue 5

Richard Stalter¹* and Robert I Lonard²

• ¹Department of Biological Sciences, St. John’s University, USA
• ²Department of Biology, University of Texas-Rio Grande Valley, USA

Received: May 20, 2024; Published: May 28, 2024

*Corresponding author: Richard Stalter, Department of Biological Sciences, St. John’s University, 8000 Utopia Parkway, Queens, NY11439, USA

DOI: 10.26717/BJSTR.2024.56.008904

Abstract PDF

Atriplex patula L. is a facultative halophyte that tolerates low to moderate levels of salinity and occurs on the margins of coastal salt marshes, roadsides, in agricultural fields, and in other areas where disturbance has occurred. The genus Atriplex L. is represented by about 250 species globally and has recently been included in the family Amaranthaceae subfamily Chenopodioidae. Atriplex patula was possibly introduced in North America from Europe, Asia or North Africa in the 18th century. Because the stems and leaves accumulate and store heavy metal pollutants, A. patula has been suggested for use in habitat remediation.

Keywords: Spear Orach; Taxonomy; Geographical Distribution; Dimorphic Seeds; Germination; Facultative Halophyte; Physiological Ecology; Range of Habitats

The genus Atriplex L. is represented by about 250 species globally. Molecular and morphological data have provided some evidence supporting the inclusion of the Chenopodiaceae in the family Amaranthaceae with the former family Chenopodiaceae now listed as a subfamily Chenopodioideae [1]. However, Welsh et al. [2] and others still use the nomen Chenopodiaceae in systematic treatments. Atriplex patula L. (spear orach, spearscale) is a facultative halophyte that tolerates low to moderate levels of soil salinity [3]. It is a widespread weedy species that occurs in agricultural fields, on roadsides, on the margins of coastal salt marshes, and in other areas where disturbance has occurred. Atriplex patula produces dimorphic seeds which allows the species to be established in unstable habitats [4, 3]. Welsh [1] indicated that A. patula was possibly introduced in North America from Europe, Asia, or North Africa in the 18th century, and its occurrence has been documented in at least 10 provinces in Canada and 29 states in the U.S.A. Chetina et al. [5] have reported that A. patula occurs in saline sites at 59º N near Perm Krai, Russia, and De Cauwer et al. [6] noted that this species is a weed control problem in sugar beet fields in Belgium. Atriplex patula has been suggested for use in habitat remediation because stems and leaves accumulate and store heavy metal pollutants [7]. Herein, we summarize important aspects of this widespread facultative halophyte.

Synonymy of the Atriplex patula complex is in a state of confusion. Synonyms of Atriplex patula L. (spear orach, spreading orache, spearscale) in North America have primarily been listed as Atriplex hastata L. subsp. patula (L.) S. Pons, A. hastata var. patula (L.) Farwell, and Teutiopsis patula (L.) Selak [1], whereas Correll and Correll [8] listed A. patula L. as A. patula L. var. hastata (L.) Gray. The nomens A. prostrata Boucher and A. hastata L. sensu Aellen non L. have also been listed as synonyms by Stalter and Lamont [9]. The following taxonomic description of A. patula is summarized from treatments of the species by Correll and Correll, [8], Stalter, [10], Taylor and Wilken, [11], and Welsh, [1]. Atriplex patula is a monoecious annual with a root system that typically extends between 10 to 18 cm below the substrate surface. Stems are erect and branched, glabrous to scaly, and range from 30 cm to 1.5 m in height. Leaves are opposite below and alternate above.

Petioles of lower leaves are up to half as long as the blades. Blades are bright green, 2.5 to 7.0 cm long and nearly as broad, truncate at the base, and acute or obtuse at the apex. The staminate flowers bearing 5 tepals and 5 stamens are borne in a terminal spike or panicle. The pistillate flowers are usually borne in few-flowered axillary or spike-like cymes. Pistillate flowers have 2 stigmas, and the base of the ovary is enclosed in a pair of bracts often reddish at maturity and up to 7 mm long. Seeds are dimorphic. Brown seeds are 2.5 to 4.0 mm wide, and black seeds are 1.0 to 2.0 mm wide. Chromosome numbers for the A. patula complex are 2n = 18 and 2n = 36. In the Netherlands, Van Der Meyden [12] tentatively recognized A. patula L. and A. hastata L. as separate species. However, he noted that there are no sharp distinctions between the two taxa, and numerous overlapping morphological variations exist in leaf blade morphology between the two entities. Van Der Meyden [12] stated that different ploidy levels occur in the complex. Atriplex hastata is a diploid and A. patula is a tetraploid.

Atriplex patula is an annual, weedy, facultative halophyte that has a wide distributional range in North America, Europe, North Africa, and Asia. Correll and Correll [8] reported its range in North America from Newfoundland westward to British Columbia in Canada, and from Newfoundland to South Carolina in the U.S.A. Stalter et al. [13] reported the occurrence of the species in coastal sites in northern Florida. On the Pacific coast of North America, it occurs from British Columbia to California. Ungar [3] indicated that it occurs in low to moderately saline sites in Kansas and Nebraska, and Correll and Correll [8] and Proffitt et al. [14] stated that A. patula is often present in saline sites in Texas and Louisiana. Atriplex patula in widespread in Europe. De Cauwer et al. [6] reported that A. patula is a weed control problem in sugar beet fields in Belgium, and Chetina et al. [5] reported the occurrence of this species in salinized alluvial soils at 59º N latitude at Perm Krai, Russia.

Atriplex patula is a weedy, facultative halophyte that occurs in a wide variety of soil types including sandy loams and clays [6], salt impacted alluvial soils [5, 15], and water-logged soils [16]. In sugar beet fields in Belgium, De Cauwer et al. [6] reported that the species is less common in acid sandy soils and is less tolerant to drought than to water-logging. Ungar [3] indicated that A. patula is a summer annual in the Central U.S.A. and can tolerate moderately saline soils under field conditions ranging from 2 ppt to 13 ppt total salts. In North Carolina, Stalter and Lamont [9] stated that habitats for A. patula are beaches and upper margins of brackish and salt marshes. In New England salt marshes, Rand [17-19] reported that this species is usually found in bare areas in the mid to high marsh in topographic zones usually dominated by Juncus gerardii or Iva frutescens. She noted that the annual halophyte Salicornia europaea may compete with A. patula in this harsh physical environment. Proffitt et al. [14] found a similar case in salt marshes in Louisiana where A. patula occurs in bare patches within sites dominated by Sporobolus alterniflorus (Spartina alterniflora).

Atriplex patula has Kranz anatomy in leaves which is indicative of the associated C₄ carbon fixation pathway of photosynthesis [1]. The C₄ pathway increases efficiency of CO₂ usage and subsequent carbon fixation. Salinity is an important factor that affects imbibition of water in seeds, germination, root elongation, and overall plant vitality [20]. NaCl in the substrate affects osmotic balance and specific ions. Salinization influences the production of the low molecular weight amino acid proline in A. patula leaves. Proline acts as an antioxidant and protects cellular protein structure and ultimately increases A. patula resistance to salt in acidic soil conditions [5].

Two types of seeds occur in A. patula. One is black and ranges in size from 1.0 to 2.0 mm in diameter, and the other seed type is brown and ranges in diameter from 1.3 to 3.0 mm [4, 3, 1]. Large brown seeds have three times the mass of smaller black seeds, a thin seed coat, a larger embryo, and absorbs water 100 times faster than unscarified black seeds [20-21]. Nurse et al. [21] stated stated that seed dimorphism enhances survival of the species in variable habitats. Larger brown seeds have a limited dormancy period and germinate rapidly in spring. However, brown seeds are more susceptible to fungal attack than black seeds [21]. Ungar [22] reported that black seeds have a hard seed coat, a long dormancy period, and scarification is required to break dormancy. In the laboratory, unscarified black seeds did not germinate. However, 73% of scarified black seeds germinated [4, 22]. Black seeds have greater resistance to high salinity stress than brown seeds and retain their viability longer than brown seeds [21]. In the laboratory, Ungar [22] found that seeds germinated and seedlings survived salinity concentrations up to 20 ppt. Germination was reduced at salinity values greater than 10 ppt, and germination declined to 17% of controls at 20 ppt. Ungar [22] also noted that seeds are less inhibited to high salinity levels that growing seedlings. In Oregon, Keammerer and Hacker [23] stated that A. patula seed viability was 91% in the high intertidal zone, but they did not mention seed dimorphism.

Atriplex patula does not fare well in competition with taller or more aggressive species in salt marshes. Minchinton et al. [24] reported that the common reed (Phragmites australis), in the upper margins of New England salt marshes, modifies soil and light conditions and produces a heavy cover of litter. These factors exclude the perennial Solidago sempervirens and the annual A. patula from this topographic zone. Atriplex patula seedling establishment and survival of mature plants only occurs at sites that have not been invaded by P. australis. A chrysomelid beetle (Erynephala maritima) is a herbivore that damages A. patula and the succulent annual halophyte Salicornia europaea in salt marshes in Rhode Island [25]. Damage to A. patula is extensive at mid-tidal elevations which are frequently inundated [17]. She also found that A. patula plants are more extensively damaged when they are not present in dense stands of S. europaea [17]. In field plots cleared of S. europaea beetle herbivory reduced A. patula survival by about 50% and reduced reproduction by 37% [18, 19].

Atriplex patula is a species that removes significant amounts of Na ions from salt-impacted soils and stores salt in cellular vacuoles in stems and leaves [15]. They noted that the deep root system improves soil quality and soil permeability in oil field brine spill sites in Saskatchewan, Canada. Mature plants are removed of spill sites and are disposed off-site. High seed production insures a standing crop in the next growing season.

Vickerman et al. [7] examined A. patula for potential habitat improvement and phytoremediation of the heavy metal Se. They found that phytoremediation was greatest in saline sites having low to moderate levels of sulfate. They also indicated that mature plants could be mechanically harvested and disposed off-site.

Atriplex patula is an aggressive annual weed in sugar beet fields in Belgium. Various herbicides have been used to control the species. However, this species exhibits high intraspecific variation in herbicide sensitivity and weed control by herbicides has been shown to be difficult [6]. Atriplex species produce extensive amounts of windblown pollen and may play a role in allergic sensitization [26]. Ferrer et al. [27] noted that pollen of A. patula extracts should be used in a battery of potential allergens for use in diagnosis and treatment of respiratory allergies in patients.

We thank Matt Toska and Menahil Shahid undergraduate research students for obtaining reference articles and St. John’s University for providing publication expenses.

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