## 2 Phylogenetic Variations in Cd Accumulation in Plants  
Plants have adapted to a variety of environments, from deserts to oceans. They are gathered into five major groups: algae, bryophytes, pteridophytes, gymnosperms, and angiosperms. The characteristics of Cd accumulation have been described in many crop species like rice [11], barley [12], and rapeseed [13]. All these studies demonstrate that Cd accumulation varies among different plant species and even within different genotypes of the same species [10]. To further understand the characteristics of Cd accumulation across the plant kingdom, the phylogenetic variation in Cd accumulation was summarized for different phyla based on the previously published research data. Algae constitute important components of our environment and ecosystem as primary producers and contribute nearly 40% of the global biomass productivity. A comparative study on the biosorption of Cd by 30 strains of algae demonstrated that algae species have the ability to absorb Cd from the environment in a species-dependent manner [14]. [PERSON] et al. [15] reported that two freshwater microalgae, _Chlorella pyrenoidosis_ and _Scenedesmus acutus_, showed 45.45% and 57.14% removal of Cd from initial Cd concentration of 1.5 ppm, and _Chlorella pyrenoidosis_ exhibited higher Cd bioaccumulation (3%) capacity than _Scenedesmus acutus_ (1.5%). In addition, the marine brown algae (Ochrophyta) _Ecklonia radiata_ was shown to uptake 660-1634 mg/g Cd of dry biomass [16]. Such high capacity of algae for Cd\({}^{2+}\) uptake might be attributed to the high alginate content in the cell wall matrix [17]. On the other hand, the ability of algae to uptake Cd\({}^{2+}\) is strongly influenced by water pH. For instance, the marine brown algae _Ecklonia radiata_ exhibited the highest uptake of Cd\({}^{2+}\) at pH 4.0 (1634 mg/g Cd of dry biomass) but the lowest uptake at pH 1.5 (660 mg/g Cd of dry biomass) when the strains were grown under Cd condition at pH 1.5-6.15 [16]. However, two green algae, _Pseudokircheniella subcapitata_ and _Scenedensulus obliquus_, were found to show the highest Cd uptake capacity at pH 7.0 [18; 19]. These results suggest that different algae species may require the specific optimal pH value for their uptake of Cd. Bryophytes are among the earliest green plants to colonize the terrestrial environment and have achieved great ecological success in various habitats, from desert to aquatic and from tropical to arctic, since evolving \(\sim\)500 Mya [20], and they are usually divided into three large clades: liverworks (Marchantiophyta), mosses (Bryophyta), and hornworks (Anthocerophyta) [21]. Mosses and liverworts possess the characteristics of lacking the cuticle layer and having pronounced ion-exchange abilities and large surface-to-weight ratio, which endow them with the ability to absorb heavy metal ions through the entire surface (reviewed by [22]). Thus, both mosses and liverworts are used as biomonitors or bioindicators of heavy metal pollution in both terrestrial and aquatic environments due to the characteristics mentioned above [22; 23]. Nevertheless, such abilities are highly species-specific. [PERSON] et al. [24] reported that two moss species, _Bryum capillare_ and _Ceratodon purpureus_, could accumulate Cd up to 0.1% of their dry weight (approximately 1125-1250 mg/kg) in their shoots, whereas [PERSON] et al. [25] detected a very small amount of Cd (ranging from 0.1 to 7.3 mg/kg, with an average value of 1.3 mg/kg) in two other moss species, _Fabronia ciliaris_ and _Leskea angustata_[25]. In addition, the biosorption of Cd by mosses is also strongly dependent on the environmental conditions. It was found that low pH values not only reduced the extracellular binding of Cd but also inhibited the intracellular uptake of Cd in the moss species _Rhytidiadelphus squarrosus_[26]. Ferns and lycophytes constitute the largest vascular plant groups besides seed plants and consist of approximately 10,578 and 1338 species, respectively [27].