Malvaceae is one of the flowering plants, which has been divided into nine subfamilies, containing about 244 genera, and 4225 species [1], distributed in tropic and subtropical regions and all over the world. This family includes the economically important plants such as cotton, okra and other ornamental shrubs. Genus Abutilon Mill. belongs to subfamily Malvoideae, Malvaceae family, comprising about 200 species, annual or perennial herbs and shrubs or even small trees, distributed in tropics and subtropics of the Americas, Africa, Asia, and Australia. The genus has significant importance, this is due to the fibbers and they contain different chemical compounds such as flavonoids, sterols, triterpenes, anthocyanins and fatty acids [2] [3].

Bentham and Hooker [4] divided Malveae into four subtribes based on the carpel arrangement, the number and position of ovule per carpel: Abutilinae, Malopinae, Malvinae, and Sidinae. While Hutchinson Hutchinson [5] reclassified Malvaceae and its tribes by combined the two subtribes Abutilinae and Sidinae into tribe Abutileae. Fryxell [6] placed Herrisantia, Robinsonella and Sida alliances into the genus Abutilon. The tribes (Abutileae and Malveae) were included in the system of [7]. [8] separated the two subtribes Malveae and Sidinae based on molecular data from Malveae under tribe Sidieae. The only one of Abutilon is poorly understood that belongs to infrageneric classification.

Several scientists have observed different species number in genus Abutilon. Baker [9] mentioned 172 species, Mattei [10] counted 100 species, while Hutchinson [5] and Husain and Baquar [11] recorded more than 400 species in genus Abutilon. Mabberley [12] reported 100 species, whereas Fryxell [13] stated around 160 species in genus Abutilon.

Taxonomic studies have been reported on Abutilon Mill. by several authors. El Naggar [14] studied pollen morphological characters of 21 species of Egyptian Malvaceae including 2 species for Abutilon: (Abutilon theophrasti Medik. and A. pannosum (G. Forst.) Schledt.), while Shaheen, et al. [15] studied pollen morphology for nine species of Abutilon. Taia [2] recorded five species of Abutilon in Saudi Arabia (A. bidentatum Hoch, A. figarium Webb, A. fruticosum Guill & Perr., A. hirtum Don and A. pannosum Schlecht.) based on morphological characters of leaves, flowers and fruits.

Floral characters are important features used to identifying and describe Abutilon plants as many Angiospermae plants. Flowers were described in several characteristics such as: size, stigma, stamens (number of stamens, forming a staminal tube around the style), number and colour of petals and sepals, length of petioles, bracteate, pedicellate, hermaphrodite, pentamerous, axile placentation [16] [17] [18] [19] [20]. Fruits are one of the most important parts that distinctive Abutilon species from each other. Many authors [11] [16] [17] [18] [20] [21] [22] [23] [24] were used fruit characters to distinguish Abutilon species such as shape, size, number of seed and carpels and present or absent of awn in carpels. Therefore, the main objectives of this study are to provide constant and reliable diagnostic characters by using numerical taxonomic methods and morphological characters, and to compare the results obtained from the morphological and morphometric data.

Some morphological characters can be used in the field to differentiate Abutilon species from each other such as: habit, plant colour, leaf structures, flower colour and fruit features. This study distinguished six species of Abutilon (A. fruticosum, A. bidentatum, A. hirtum, A. figarianum, A. grandifolium and A. Pannosum) that were collected from different locations of Saudi Arabia based on morphological and morphometric data.

The A. fruticosum species is well known in Saudi Arabia and were reported by previous authors (Collenette 1985, 1999; Migahid 1996; Chaudhary 2001; Taia 2009). Collenette (1999) cited two taxa affinities to A. fruticosum species and she called one A. sp. aff. fruticosum and the second A. sp. nov. aff. fruticosum. However, our study’s findings did not agree with these taxa affinities. Plants of this species are distributed in the central and from north-western to southwestern of Saudi Arabia (Table 1 and Figure 16) and they are distinguished by several characters, colour of leaf is grayish green (Figure 2(B)), leaf shape is ovate to broadly ovate (Figure 3(B)), leaf surface is glabrous (Figure 4(A)), leaf apex is acute to cuspidate (Figure 5(C)), leaf base is cordate (Figure 6(A)), leaf margin is entire (Figure 7(C)), colour of flower is yellow pale (Figure 8(B)), fruit

shape is cylindric (Figure 9(B)), the mericarp is reniform with pointed apex (Figure 10(B)).

Species of A. bidentatum is also well known in Saudi Arabia and was recorded by previous authors (Collenette 1985, 1999; Migahid 1996; Chaudhary 2001; Taia 2009). Collenette (1999) reported two taxa affinity to A. bidentatum species and she called one A. sp. aff. bidentatum and the second is A. sp. nov. aff. bidentatum. However, our study’s findings did not agree with these taxa affinities. Plants of this species are distributed in the western to southern regions of Saudi Arabia (Table 1 and Figure 16) and they are distinguished by several characters, colour of leaf is yellowish green (Figure 2(C)), leaf shape is ovate to broadly ovate (Figure 3(B)), leaf surface is pubescent to tomentosa (Figure 4(C)), leaf apex is cuspidate (Figure 5(B)), leaf base is cordate (Figure 6(A)), leaf margin is double denticulate to dentate (Figure 7(B)), colour of flower is yellow (Figure 8(A)), fruit shape is cylindric (Figure 9(B)), the mericarp is reniform with pointed apex (Figure 10(B)).

Species of A. hirtum was recorded by previous authors such as: Collenette 1999; Migahid 1996; Chaudhary 2001; Taia 2009. Plants of this species are distributed western and in the southern region of Saudi Arabia (Table 5 and Figure 16) and they are distinguished by several characters, colour of leaf is green (Figure 2(A)), leaf shape is ovate to broadly ovate (Figure 3(B)) leaf surface is velvety (Figure 4(B)), leaf apex is acute to cuspidate (Figure 5(C)), leaf base is cordate (Figure 6(A)), leaf margin is double denticulate to dentate (Figure 7(B)), colour of flower is yellow pale (Figure 8(B)), fruit shape is cylindric (Figure 9(B)), the mericarp is reniform with pointed apex (Figure 10(B)).

Species of A. figarianum was recorded by previous authors such as: Collenette 1999; Migahid 1996; Chaudhary 2001. Taia (2009) cited incorrect scientific name of A. figarium, the correct scientific name is A. figarianum. Plants of this species are distributed in the southern and western to southwestern regions of Saudi Arabia (Table 1 and Figure 16) and they are distinguished by several characters, colour of leaf is green (Figure 2(A)) but sometimes in some samples yellowish green (Figure 2(C)), leaf shape is ovate to broadly ovate (Figure 3(B)), leaf surface is pubescent to tomentosa (Figure 4(C)), leaf apex is cuspidate (Figure 5(B)), or sometimes acute (Figure 5(A)) or acute to cuspidate (Figure 5(C)), leaf base is cordate to truncate (Figure 6(C)) sometimes cordate (Figure 6(A)), leaf margin is double denticulate to dentate (Figure 7(B)), colour of flower is yellow (Figure 8(A)), fruit shape is globose (Figure 9(A)) and the mericarp is reniform with rounded apex (Figure 10(A)).

The species of A. grandifolium was previously reported by Chaudhary (2001) only. Collentte (1985, 1999) nor Taia (2009) recorded this species distributed in Saudi Arabia. Plants of this species are distributed in the western region (Table 1 and Figure 16) and they are distinguished by several characters, colour of leaf is green (Figure 2(A)), leaf shape is ovate to broadly ovate (Figure 3(B)) in some specimen are cordate (Figure 3(B)), leaf surface is hairy (Figure 4(D)), leaf apex is cuspidate (Figure 5(B)), leaf base is cordate (Figure 6(A)), leaf margin is double denticulate to dentate (Figure 7(B)), colour of flower is yellow (Figure 8(A)), fruit shape is cylindric (Figure 9(B)) and the mericarp is reniform with pointed apex (Figure 10(B)).

The species of A. pannosum is well known in Saudi Arabia and was reported by previous authors (Collenette 1999; Migahid 1996; Chaudhary 2001; Taia 2009). Plants of this species are widespread in Saudi Arabia, from north-western to southwestern of the country and in the eastern region (Table 1 and Figure 16) and they are distinguished by several characters, there is a variation of leaf formation in this species. Its Colour of leaf is green (Figure 2(A)) sometimes yellowish green (Figure 2(C)), leaf shape is ovate to broadly ovate (Figure 3(B)) sometimes in some specimens is cordate (Figure 3(A)), leaf surface is pubescent to tomentosa (Figure 4(C)) but sometimes is velvety (Figure 4(B)), leaf apex is differ, it can be cuspidate (Figure 5(B)) or acute to cuspidate (Figure 5(C)) obtuse (Figure 5(D)) and sometimes acute (Figure 5(A)), leaf base is also differ, cordate (Figure 6(A)) or truncate (Figure 6(B)) and cordate to truncate (Figure 6(C)), leaf margin is double denticulate to dentate (Figure 7(B)) and sometime double serrate (Figure 7(A)), colour of flower is consistent color, its yellow with red center (Figure 8(C)), and the fruit shape is globose (Figure 9(A)), the mericarp is reniform with rounded apex (Figure 10(B)).

The numerical taxonomy based on the morphological characters including quantitative and qualitative in the PCoA and the UPGMA analysis and based on quantitative characters in the PCO analysis indicated that the Abutilon plants under this study distinguished into six groups with realistic agreement in all analysis results. The results of the UPGMA analysis (Figure 11) separated all 43 examined samples into three main clusters. First cluster includes all plants of A. grandifolium and A. figarianum, second cluster includes all plants of A. hirtum, A. bidentatum and A. fruticosum, while all 34 plants of the A. pannosum species are located in the third cluster. In the PCoA based on 26 quantitative and 10 qualitative characters (Figure 12(A) and Figure 12(B)) and PCA analyses based on only 26 quantitative morphological characters (Figure 13) of the Abutilon accessions are clearly separated into six main groups in the axis one and three (Figure 12(A) and Figure 12(B); Figure 13). The group 1 includes three samples of A. grandifolium species, likewise, group 2 includes three samples of A. figarianum species, while only one sample of A. hirtum in group 3, A. bidentatum in group 4, A. fruticosum in group 5 and 34 samples of A. pannosum species gathered in group 7 (Figure 12(A) and Figure 12(B); Figure 13).

This current study provides the morphological characteristics which are effective in Abutilon species identification. Six species of genus Abutilon were distinguished and identified using morphological characteristics and morphometric analysis of the PCoA, the UPGMA and the PCA.

Ethical approval is not required for this type of research.

The authors received no financial support for the research.

Thanks to Maryam Alshebramy, Salehm Algharbi, Amer Alasiri, Muhammed Althawabi, Muhammed Almalki, Muhammed Alshawi for their help during field trips.

The authors declared no conflict of interest.

Alzahrani, D.A., Albokhari, E.J. and Khoj, A. (2021) Taxonomic Studies on Some Members of the Genus Abutilon Mill. (Malvaceae). American Journal of Plant Sciences, 12, 199-220. https://doi.org/10.4236/ajps.2021.122012