African Journal of
Plant Science

  • Abbreviation: Afr. J. Plant Sci.
  • Language: English
  • ISSN: 1996-0824
  • DOI: 10.5897/AJPS
  • Start Year: 2007
  • Published Articles: 761

Full Length Research Paper

Taxonomic significance of the vegetative anatomy of members of genera Colocasia (L.) Schott and Xanthosoma (L.) Schott in the family Araceae

Oluwabunmi Okerinmola Arogundade
  • Oluwabunmi Okerinmola Arogundade
  • Department of Botany, Faculty of Science, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.
  • Google Scholar
Olubukola Adedeji
  • Olubukola Adedeji
  • Department of Botany, Faculty of Science, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.
  • Google Scholar


  •  Received: 30 January 2019
  •  Accepted: 14 March 2019
  •  Published: 30 April 2019

 ABSTRACT

Anatomical attributes are important for taxonomic studies of plants.  This study investigated foliar and petiole anatomy of some members of the genera Colocasia and Xanthosoma. Similar and diagnostic characters critical for the taxonomy of the two genera were identified. The similar characters include, polygonal epidermal cell shape, straight adaxial anticlinal wall pattern, brachyparacytic stomata type, elliptic shaped stomata and unmodified raphide type. The presence of papillae on the adaxial surfaces of the members of genus Colocasia but not in the Xanthosoma taxa; lamellar collenchyma type in Xanthosoma mafaffa (Red), and unicellular non-glandular trichomes in Xanthosoma mafaffa (White) were recorded as diagnostic characters.

 

Key words: Brachyparacytic stomata, collenchyma, druses, foliar anatomy, petiole anatomy, papillae, raphides, trichome.


 INTRODUCTION

Anatomical methods have been found to be very useful in many taxonomic investigations. Several authors have employed leaf, petiole, and even wood anatomical characters that are not influenced by the environment in solving taxonomic problems among groups of plants (Adedeji and Illoh, 2004; Adedeji et al., 2007; Thakuri and Patil, 2011; Akinloye et al., 2012; Oladipo and Oyaniran, 2013; Akinnubi et al., 2014; Osuji and Nwala, 2015; Mudasiru et al., 2016; Rodriguez et al., 2016; Arogundade and Adedeji, 2017). The Araceae is a large family of plants, found in the New World and Old World tropics, and north temperate regions (Vargas et al., 2004; Mora et al., 2006). Members of the family are known as Ariods (Bown, 2000). Although research works have been carried out on the Araceae to settle some taxonomic positions of genera, more research is needed to resolve persistent confusions reported among lower ranks in the family (Green and Oguzor, 2009). According to Keating (2003), leaf and petiole anatomy of the Araceae have a high potential use as character states in resolving taxonomic problems in the family.
 
Colocasia (L.) Schott, tribe Colocasieae, and Xanthosoma (L.) Schott, tribe Caladieae, are two genera in the family Araceae. They grow  in  different  ecological zones of the world (Croat, 1990). There are 3,750 species of aroids from 114 genera according to Petruzzello (2018), though Boyce and Croat (2018) reported 3,645 species from 144 genera. Members of these two genera, Colocasia and Xanthosoma, are important sources of food and medicine, especially in rural and poor communities where food security is posing a major challenge (Matemilola and Elegbede, 2017).
 
An interesting feature or character of aroids is their toxicity. Their cells possess calcium oxalate crystals in form of raphides and druses (Franceschi and Nakata, 2005; Arogundade and Adedeji, 2017). Therefore, Araceae members are enlisted as poisonous plants (Mulligan and Munro, 1990). Nevertheless people had devised methods for eliminating the poison to make these edible (Okiy, 1960; Ibe and Iwueke, 1984; Amanze, 2009). The corms and leaves of members of genera Colocasia and Xanthosoma have been part of delicacies around the world (Cable, 1984; Okeke, 1992, Amanze, 2009).
 
Morphological descriptions of these two genera have been studied (Purseglove, 1972; Burkill, 1985; Gill, 1988; Mayo et al., 1997; Ngoka, 1997; Bown, 2000), resolving some descriptive problems between the two genera. A ready distinction between Xanthosoma and Colocasia as ascertained by Burkill (1985), lies in the junction of the leaf lamina with the petiole. The leaf is attached to the petiole on the leaf margin in Xanthosoma, while in Colocasia, the attachment is towards the centre. That is, unlike the leaves of Colocasia, those of Xanthosoma are usually not peltate—the upper v-notch extends in to the point of attachment of the leaf petiole to the blade.
 
The genus Colocasia include six species of tuberous perennials from tropical Asia, grown there as a staple starchy food. Common names include Elephant-ear, Taro, Cocoyam, Dasheen, and Eddoe. Colocasia esculentum has between 28 and 42 chromosomes per cell that behave erratically during cell division. Thus, new permutations, resulting in new varieties are being formed without recourse to cross-pollination and seed production (Onwueme, 1978). Although cultivated plants rarely bloom, they are cultivated all the year round in subtropical and tropical areas. Taro is closely related to Xanthosoma and Caladium, which are commonly grown as ornamentals (Bown, 2000).
 
The genus Xanthosoma is a group of fleshy herbaceous stem-less plant with leaves arising from the crown of a central corm usually surrounded by a mass of cormels. A number of varieties exist based on yield, the colour of the flesh or skin, size of corm, storage quality, palatability and so on. The young leaves are eaten as a green vegetable (Kay, 1987). Mayo et al. (1997) reported chromosome number 2n = 22, 26, 39 and 52 for the genus.
 
This work is intended to shed more light on taxonomy of genera Colocasia and Xanthosoma which has been reported to be confusing (Green and Oguzor, 2009) usingtheir leaf and petiole anatomical characters.


 MATERIALS AND METHODS

Five taxa from the genera Colocasia and Xanthosoma were included in this work. The species and varieties are: C. esculentum var. esculentum (L.) Schott, C. esculentum var. antiquorum (L.) Schott, the red and white varieties of X. mafaffa Schott and X. saggitifolium Schott. The taxa were collected from different locations in the South Western part of Nigeria and were authenticated at Forestry Herbarium Ibadan (FHI), Oyo State and IFE Herbarium at Obafemi Awolowo University, Osun State, Nigeria. Voucher specimen was deposited at the IFE herbarium (Table 1).
 
 
Epidermal studies
 
The well expanded median portion of the leaf of each of the taxa was scrapped following the standard method described by Metcalfe (1960) and as adopted by Arogundade and Adedeji (2016). Epidermal peels from both the adaxial and abaxial surfaces were obtained and afterwards stained with Safranin O. The peels were later mounted in dilute glycerine in readiness for microscopic examination. Features observed on the epidermal peels included the epidermal cell shape, the anticlinal wall patterns, stomata shape and size. The stomata area was calculated by multiplying the length and breadth of 50 stomata from at least five different plant accessions. Stomata indices of the adaxial and abaxial surfaces were calculated using the formula: 
 
 
Where S = Number of stomata and E = Number of ordinary epidermal cells plus the subsidiary cells in the same unit area.
 
Photomicrographs of the epidermis were taken for both the adaxial and the abaxial surfaces.
 
Petiole anatomy
 
A Reichert sliding microtome manufactured at Vienna, Austria NR. 367 019 was employed in cutting the transverse section of the petiole of the taxa at the proximal, median and distal regions. The sections were made at a thickness of 8 – 15 µm. For staining, Safranin O and Alcian blue stains were used. After which differentiation and dehydration were carried out on the sections by passing them through varying percentages of ethanol (50%, 70%, 80%, 90% and absolute). The sections were later mounted in 25% glycerine and observed under the microscope Olympus XSZ-107BN binocular biological microscope manufactured by Zenith Laboratories, California. Photomicrographs of the different sections were taken.
 
All microscopic measurements were taken with the aid of an ocular micrometer inserted into the eyepiece of a microscope. They were later multiplied by the ocular constant with respect to the power under which they were taken in order to convert them to micrometer.


 RESULTS

Tables  2  and  3  show  the  summary  of   the  important  qualitative foliar epidermal features of the adaxial and abaxial surfaces respectively while Table 4 shows the summary of the quantitative foliar anatomical features.
 
Adaxial epidermal characteristics
 
In C. esculentum var. antiquorum, epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 213.12 and 532.8 µm2 (mean  =  348.68 µm2). Brachyparacytic stomata types, elliptic in shape, were observed (Plate 1A and B). Stomata size ranges between 116.55 and 179.82 µm2 (mean = 141.59 µm2) and stomata index ranged between 4.47 - 8.89% (mean = 6.87%). Druses and papillae were present.
 
 
 
 
In C. esculentum var. esculentum, epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 336.6 and 761.6 µm2 (mean = 536.79 µm2). Brachyparacytic, occasionally anisocytic stomata types,  elliptic   in  shape,  were  observed  (Plate 1F). Stomata size ranges between 142.8 and 214.2 µm2 (mean = 175.24 µm2) and stomata index ranges between 2.70 and 7.59% (mean = 4.75%). Papillae were present.
 
In X. mafaffa (Red variety), epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 214.2 and 578.0 µm2 (mean = 391.20 µm2). Brachyparacytic, occasionally anomocytic stomata types, elliptic, occasionally circular in shape were observed (Plate 1I and J). Stomata size ranges between 183.6 and 299.2 µm2 (mean = 242.49 µm2) and stomata index ranges between 4.33 - 8.33% (mean = 6.56%). Cuticular striations radiating from the guard cells were present.
 
In X. mafaffa (White Variety), epidermal cells were polygonal with straight anticlinal wall. They also varied in size, shape and arrangement. Epidermal cell area ranges between 261.8 and 652.8 µm2 (mean = 455.81 µm2). Brachyparacytic, occasionally anomocytic stomata types, elliptic in shape were observed (Plate 1M). Stomata size ranges between 183.6 -285.6 µm2 (mean = 216.38 µm2) and stomata index ranges between 4.41 and 7.32% (mean = 5.66%).
 
In X. saggitifolium, epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 309.4 and 1142.4 µm2 (mean = 745.62 µm2). Brachyparacytic stomata types, elliptic in shape, were observed (Plate 1O). Stomata size ranges between 261.8 and 397.8 µm2 (mean = 312.32 µm2) and stomata index ranges between 3.16 - 8.51% (mean = 5.67%).
 
Abaxial epidermal characteristics
 
In C. esculentum var. antiquorum, epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 139.86 and 439.56 µm2 (mean = 261.21 µm2). Brachyparacytic, occasionally anomocytic stomata types as well as two stomata sharing the same subsidiary cells, were observed. Stomata were elliptic in shape though occasionally circular (Plate 1C, D and E). Stomata size ranges between 149.85 -266.4 µm2 (mean = 173.36 µm2) and stomata index ranges between 8.15 and 14.78% (mean = 10.51%). Papillae and druses are present.
 
In C. esculentum var. esculentum epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 219.78 and 799.2 µm2 (mean = 419.98 µm2). Brachy-paracytic, occasionally anomocytic stomata types, elliptic in shape, though occasionally circular were observed (Plate 1G and H). Stomata size ranges between 159.84 and 233.1 µm2 (mean = 192.87 µm2) and stomata index ranges   between    9.42   and   13.13%  (mean  = 11.31%). Papillae were present.          
 
In X. mafaffa (Red variety) epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 166.6 and 442.0 µm2 (mean = 311.85 µm2). Brachyparacytic stomata types, elliptic in shape though occasionally circular, were observed (Plate 1K and L). Stomata size ranges between 183.6 and272.0 µm2 (mean = 215.02 µm2) and stomata index ranges between 11.98 and 15.60% (mean = 13.37%). Papillae with cuticular striations radiating from the guard cells were present.
 
In X. mafaffa (White variety) epidermal cells were polygonal with straight anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 214.2 and 652.8 µm2  (mean  =  428.13 µm2). Brachyparacytic, occasionally anomocytic stomata types, elliptic in shape, though occasionally circular were observed (Plate 1N). Stomata size ranges between 183.6 and 244.8 µm2 (mean = 212.16 µm2) and stomata index ranges between 8.78 and 12.65%; (mean = 10.78%). Papillae with cuticular striations radiating from the guard cells were present.
 
In X. saggitifolium epidermal cells are polygonal to irregular with straight to wavy anticlinal wall. They varied in size, shape and arrangement. Epidermal cell area ranges between 261.8 and 867.0 µm2 (mean = 564.6 µm2). Brachyparacytic, occasionally anomocytic stomata types, elliptic in shape were observed (Plate 1P). Stomata size ranges between 238.0 and 367.2 µm2 (mean = 305.66 µm2) and stomata index ranges between 11.11 and 16.79%  (mean = 13.67%). Papillae with cuticular striations radiating from the guard cells were present.
 
Petiole anatomy
 
The summary of the proximal, median and distal regions of the petiole anatomy of the taxa studied is as shown on Table 5.
 
 
C. esculentum var. antiquorum
 
The outline of the adaxial surface of the proximal region was convex while that of the median and distal regions was concave. The outline is consistently round on the abaxial side of the petiole at the three regions. The epidermis was uniseriate and it was a single layer. One to four layers of parenchyma cells were encountered at the proximal and distal regions of the petiole, while one to three layers were identified at the median region. Lacunar collenchyma cells were encountered as discontinuous bundles on both the adaxial and abaxial sides of the petiole in all the three regions except in the distal region where it was not present on the adaxial side. Air spaces of  varying   diameter   were   present   through  the  three regions of the petiole. Collateral vascular bundles were scattered throughout the ground tissue in the three regions with the xylem being consistently surrounded by one or two layers of xylem parenchyma. Unmodified and spindle-shaped raphides were present in the three regions of the petiole, starch grains were encountered in the median region while druses were found in both median and distal regions (Plates 2 to 4).
 
C. esculentum var. esculentum
 
The outline of the adaxial surface of the proximal region was convex, flat to slightly convex at the median region and concave at the distal region. The outline was consistently round on the abaxial side of the petiole at the three regions. The epidermis was uniseriate and it was a single layer. One to two layers of parenchyma cells were encountered at the three regions of the petiole. Lacunar collenchyma cells were encountered as discontinuous bundles on both the adaxial and abaxial sides of the petiole in all the three regions except in the distal region where it was not present on the adaxial side. Air spaces of varying diameter are present through the three regions of the petiole. Collateral vascular bundles are scattered throughout the ground tissue in the three regions with the xylem being consistently surrounded by a layer of xylem parenchyma. Spindle-shaped raphides were present in the three regions of the petiole, biforine raphides were observed only in the proximal region, unmodified raphide types and tannins were also observed in the distal region only while druses were present in both the median and distal regions (Plates 5 to 7).
 
 
 
 
 
 
 
Xanthosoma mafaffa (Red)
 
The outline of the adaxial surface of the proximal region was flat to slightly convex, convex at the median region and concave at the distal region. The outline was consistently round on the abaxial side of the petiole at the three regions. The epidermis was uniseriate and it was a single layer. Two to three layers of parenchyma cells were encountered at the proximal region of the petiole, while two to four layers were identified at the median and distal regions. Lamella collenchyma cells were encountered as discontinuous bundles on both the adaxial and abaxial sides of the petiole in all the three regions except in the distal region where it was absent on the adaxial side. Air spaces of varying diameter were present through the three regions of the petiole. Collateral vascular bundles were scattered throughout the ground tissue in the three regions with the xylem being consistently surrounded by one layer of xylem parenchyma. Unmodified raphides were encountered only in the median region of the petiole, starch grains were present in all the three regions, tannins were present only at the proximal region while druses were encountered at the median and distal regions (Plates 8 to 10)
 
 
 
 
X. mafaffa (White)
 
The outlines of the adaxial surface of the proximal and median regions were convex while that of the distal region was concave. The outline was consistently round on the abaxial side of the petiole at the three regions. The epidermis was uniseriate and it was a single layer. One to two layers of parenchyma cells were encountered at the proximal and median regions of the petiole, while one to three layers were identified at the distal region. Lacunar collenchyma cells were encountered as discontinuous bundles on both the adaxial and abaxial sides of the petiole in all the three regions except in the distal region where it was absent on the adaxial side. Air spaces of varying diameter are present through the three regions of the petiole. Collateral vascular bundles were scattered throughout the ground tissue in the three regions with the xylem being consistently surrounded by one layer of xylem parenchyma. Unmodified raphides were encountered in the proximal and median regions, druses and starch grains were present in the three regions of the petiole. Trichome-like (eglandular, uniseriate trichomes) structures were identified in the distal region of the petiole
(Plates 11 to 13).
 
Xanthosoma saggitifolium
 
The outline of the adaxial surface of the three regions was convex while that of the abaxial side is consistently round. The epidermis was uniseriate and it was a single layer. One to six layers of parenchyma cells were encountered at the proximal and median regions of the petiole, while four to six layers were identified at the distal region.  Lacunar  collenchyma  cells were encountered as discontinuous bundles on both the adaxial and abaxial sides of the petiole in the three regions. Air spaces of varying diameter were present through the three regions of the petiole. Collateral vascular bundles were scattered throughout the ground tissue in the three regions with the xylem being consistently surrounded by one layer of xylem parenchyma. Spindle-shaped raphides were encountered in all the three regions, while druses and starch grains were encountered in the median and distal regions (Plates 14 to 16).
 
 
 
 
 
 


 DISCUSSION

Anatomical features have been found very useful in the classification of plant species and so the use of anatomical features in separating or delimiting species is germane. This is because most  anatomical  features  are not affected or altered by the environmental factors. Anatomical research works that have been done on some species of Araceae, which include the works of Green and Oguzor (2009) on four selected species from genera Xanthosoma, Dieffenbachia and Colocasia in the South Eastern part of Nigeria; Ina and Eka (2013) on leaf surface comparison of some species in the genera Alocasia, Colocasia and Remuatia in Indonesia; Osuji and Nwala (2015) on some cultivars of Xanthosoma and Colocasia also in the South Eastern part of Nigeria, were limited to the epidermal studies of the selected species or cultivars only. This study provided some more detailed information on the epidermal surfaces of more taxa as well as the details of the transverse sections of the petioles in the three petiole regions, proximal, median and distal regions.
 
Similar and diagnostic characters which were useful tools in the taxonomy of the two genera were identified in this study. The epidermal cell shape on the adaxial and abaxial surfaces of the two varieties of Colocasia studied; C. esculentum var. antiquorum and C. esculentum var. esculentum as well as that of the three taxa in the genus Xanthosoma; X. mafaffa (Red), X. mafaffa (White) and X.  saggitifolium is polygonal. This was a common character to the two genera. Anticlinal wall pattern on the adaxial surface was straight in all the taxa of Colocasia and Xanthosoma studied. On the abaxial surface however, though the wall pattern was straight in all the taxa, it was straight to wavy in X. saggitifolium. This separated X. saggitifolium from the two varieties of X. mafaffa. Adedeji et al. (2007) also employed anticlinal wall pattern in the separation of some species in the family Solanaceae. Generally, there were more stomata on the abaxial surfaces than on the adaxial surfaces of all the taxa studied. The presence of brachyparacytic stomata complex type in all the taxa agrees with the findings of Osuji and Nwala (2015) who reported the presence of paracytic and brachyparacytic stomata types in the cultivars of Xanthosoma and Colocasia that they studied. However, additional stomata complex types were encountered on one or both surfaces of some of the taxa studied. On the adaxial surface, anisocytic stomata were found in C. esculentum var. esculentum which separated it from the other variety, C. esculentum var. antiquorum.
 
On  the abaxial surface,  anomocytic stomata were  the  additional stomata encountered in all the taxa but not in the red variety of X. mafaffa. According to Hetherington and Woodward (2003), stomata types are genetically determined and so cannot be influenced by the environment.
 
Stomata size is also quite diagnostic (Thair and Rajput, 2009). The largest stomata sizes were encountered in X. saggitifolium while the smallest sizes were encountered in C. esculentum var. antiquorum. Elliptic shaped stomata were common to all the taxa studied; notwithstanding, some of the taxa have additional circular shaped stomata especially on their abaxial surfaces. Stomata index was generally higher on the abaxial surface than on the adaxial surface in all the taxa studied. Druses of calcium oxalate crystals were found on the adaxial and abaxial epidermal surfaces of C. esculentum var. antiquorum only.   This   distinguished   it   from   C.  esculentum  var. esculentum and the members of the genus X. in this study. Adedeji and Illoh (2004) also reported a separation among some species of Hibiscus based on the presence of druses.
 
The presence of globular or spherical papillae in some of the taxa studied is of diagnostic value. Papillae were encountered on the adaxial surfaces of the two varieties of Colocasia studied, that is, C. esculentum var. antiquorum and C. esculentum var. esculentum but not on those of the three taxa of Xanthosoma. This can be employed in the delimitation of the members of the genus Colocasia from the members of the genus Xanthosoma. On the abaxial surface, however, they were encountered in all the species and varieties of the two genera. They were of variable shapes and sizes. The subsidiary cells in most of these taxa  have   no  papillae.  Osuji  and  Nwala (2015) also reported the presence of papillae on the abaxial surfaces of the X. mafaffa accessions but did not report it on the two surfaces of Colocasia. Osuji (2006) separated two species in the genus Musa based on the presence or absence of papillae.
 
Ridges or folds of the cuticle form ornamentations on them; these ornamentations largely consist of striae, hence, striated cuticle (Metcalfe and Chalk, 1979).
 
According to Solereder (1908), these striations are very useful for specific diagnosis and are not always developed in the same way on the two surfaces of the leaf, they are also taxonomically stable. Adedeji and Illoh (2004) used cuticular striations to separate some species of Hibiscus. In this study, striated cuticle was found on the adaxial surface of the red variety of X. mafaffa as well as on the abaxial surfaces of all the taxa of the genus Xanthosoma studied, that is, the red and white varieties of X. mafaffa and X. saggitifolium. However, the striation pattern on the abaxial surface of the red variety of X. mafaffa revealed a unique feature as it formed a continuous network with the papillae in such a way that it kept the stomata and epidermal cells out of focus. This is a delimiting factor among the members of the genus Xanthosoma. Also, no cuticular striations were observed in the two varieties of C. esculentum.
 
The results of the anatomy of the petiole have provided a wide range of characters that were equally of diagnostic value in delimiting the Araceae species studied. Thakuri and Patil (2011) have separated some species of the family  Euphorbiaceae  using  petiole  anatomy.  Concave adaxial petiole outline in the median region of C. esculentum var. antiquorum differentiated it from C. esculentum var. esculentum and the three members of genus Xanthosoma in this study with convex or flat to slightly convex outline. In the distal region, however, convex adaxial petiole outline separated X. saggitifolium from all the other taxa where concave adaxial petiole outline was observed. The cells of the epidermis in the petiole of all the taxa studied were of one layer and uniseriate. Parenchyma cells of varying number of layers from one to six were present in the proximal, median and distal regions of the petiole of the taxa studied.
 
All the taxa studied have the collenchyma cells as discontinuous bundles  but  the   types   and   location  of  collenchyma cells can be employed in separating them. Lacunar collenchyma cells were encountered in the two varieties of Colocasia; C. esculentum var. antiquorum and C. esculentum var. esculentum, as well as X. mafaffa (White) and X. saggitifolium whereas the collenchyma cells were the lamellar type in Xanthosoma mafaffa (Red) which separated it from the white variety and the other taxa. The collenchyma cells were observed on both the adaxial and abaxial surfaces of the proximal and median regions of all the taxa in this study. The variation observed was in the distal region where it occurred on both surfaces of X. saggitifolium and only the adaxial surfaces of the other four taxa. Collateral vascular bundles scattered in the ground tissues were found in the three regions of all the taxa studied and all the xylem cells were surrounded by xylem parenchyma. Vascular bundles are known to be scattered in the  ground  tissues  of Monocots, which is one of their major characteristics (Fahn, 1974).
 
Raphides, druses, tannins and starch grains were observed in petiole of all the taxa. The presence of raphides and druses which are calcium oxalate crystals have been well established among the members of the family Araceae (Middendorf, 1982; Mayo et al., 1997; Arogundade and Adedeji, 2016). From the work of Keating (2004), eight types of raphides have been established. They are unmodified, styloids, wide cells (a form of the unmodified raphide crystal), elongated cells, tubular cells, articulated tubes, spindle-shaped, and biforine raphides. The unmodified raphide type was observed in all the taxa studied. The spindle-shaped type was observed only in the two varieties of Colocasia and X. saggitifolium while the biforines were observed only in C.   esculentum   var.   esculentum.   This   can   also   be employed in delimiting the taxa in this study. Tannins were observed in C. esculentum var. esculentum and X. mafaffa (Red). They were not encountered in the other taxa. Where present, they were always found close to the vascular bundles.
 
Aroids, plants in the Araceae family are generally known to be glabrous. Trichomes are highly unusual in their leaves and stems (Solereder and Meyer, 1928; Mayo et al., 1997; Bown, 2000). Interestingly, in this study, some trichome-like structures were found on the adaxial side in the distal region of the petiole of X. mafaffa (White). They were more or less unicellular, non-glandular trichomes. Solereder and Meyer (1928) also reported the presence of unicellular hairs in X. pubescens. This obviously separated X. mafaffa (White) from its Red variety and the other taxa in this study.


 CONCLUSION

In conclusion, the members of genera Colocasia and Xanthosoma can be separated based on their anatomical features although many of the observed characters are common to them affirming their familial classification. Some other characters cut across the two genera. The unifying features observed include polygonal epidermal cell shape, straight adaxial anticlinal wall pattern, brachyparacytic stomata, elliptic shaped stomata and unmodified raphide type. Diagnostic features that can be employed in separating the two genera are the presence of papillae on the adaxial surfaces of the two varieties of Colocasia which were not observed on the adaxial surfaces of the Xanthosoma taxa. Also cuticular striations observed only in the members of genus Xanthosoma but not in the members of genus Colocasia. Worthy of note is the presence of unicellular non-glandular trichomes observed only in X. mafaffa (White).


 CONFLICT OF INTERESTS

The authors have not declared any conflict of interests.



 REFERENCES

Akinloye AJ, Illoh HC, Olagoke OA (2012). Significance of wood anatomical features to the taxonomy of five Cola species. Sustainable Agriculture Research 1(2):21-26.
Crossref

 Amanze KO (2009). The proximate composition and the anti-nutritive factors in seven varieties of Cocoyam (Colocasia and Xanthosoma). Journal of Research in National Development 7(2):1-6.

   

Arogundade OO, Adedeji O (2016). Foliar Epidermal Study of some Species of Aglaonema Schott (Araceae) in Nigeria. Ife Journal of Science 18(1):293-303.

   

Arogundade OO, Adedeji O (2017). Comparative Foliar and Petiole Anatomy of Some Members of the Genus Dieffenbachia Schott in the Family Araceae. Notulae Scientia Biologicae 9(1):94-103.
Crossref

   

Adedeji O, Illoh HC (2004). Comparative foliar anatomy of ten species in the genus Hibiscus L. in Nigeria. New Botanists 31:147-180.

   

Adedeji O, Ajuwon OY, Babawale OO (2007). Foliar epidermal studies, organographic distribution and taxonomic importance of trichomes in the family Solanaceae. International Journal of Botany 3(3):276-282.
Crossref

   

Akinnubi FM, Akinloye AJ, Olaleye-Otunla O, Adenegan-Alakinde TA (2014). Foliar anatomy of some species of Asteraceae in South Western Nigeria. African Journal of Plant Science 8(9):426-440.
Crossref

   

Bown D (2000). Aroids: Plants of the Arum Family. Timber Press, Portland, Oregon.

   

Boyce P, Croat BT (2018). Boyce PC, Croat TB (2011 onwards).The Überlist of Araceae, Totals for Published and Estimated Number of Species in Aroid Genera. Available at: http://www.aroid.org/genera/180211uberlist.pdf.

   

Burkill HM (1985). The Useful Plants of West Tropical Africa. Royal Botanic Gardens, Kew 2(1):193-211.

   

Cable WJ (1984). The spread of taro (Colocasia sp.) in the Pacific. In Edible Aroids. Ed. S. Chandra. Oxford: Clarendon Press. pp. 28- 33.

   

Croat TB (1990). Ecology and Life forms of Araceae. Aroideana 11(3-4):1-55.

   

Fahn A. (1974). Plant Anatomy (Second Revised Edition). Pergamon Press Ltd, Oxford, England P 7.

   

Franceschi VR, Nakata PA (2005). Calcium oxalate in plants: formation and function. Annual Review of Plant Biology 56:41-71.
Crossref

   

Gill LS (1988). Taxonomy of Flowering Plants. Africana-Fep Publishers Limited, Onitsha, Nigeria pp. 154-281.

   

 

Green BO, Oguzor C (2009). Application of Biosystematics and Nutritional Parameters in the Delimitation of Family Araceae. African Journal of Basic and Applied Sciences 1(1-2):44-48.
Crossref

 

 Hetherington AM, Woodward FI (2003). The role of stomata in sensing and driving environmental change. Nature 424:901-908.
Crossref

   

Ibe MU, Iwueke CC (1984). Production and utilization of cocoyam. Extension Bulletin No. 14, NRCRI, Umudike pp. 10-11.

   

Ina E, Eka FT (2013). Leaf surface comparison of three genera of Araceae in Indonesia. Buletin Kebun Raya 16(2):131-145.

   

Kay DE (1987). Root Crops. Second Edition (Revised by E.G.B. Gooding). Tropical Development and Research Institute, London.

   

Keating RC (2003). Leaf anatomical characters and their value in understanding morphoclines in the Araceae. Botanical Review 68:510-523.
Crossref

   

Keating RC (2004). Systematic occurrence of raphide crystals in Araceae. Annals of Botany 91(3):495-504.

   

Matemilola S, Elegbede I (2017). The Challenges of Food Security in Nigeria. Open Access Library Journal 4:e4185.

   

Mayo SJ Tomlinson PB, Bogner J, Boyce P (1997). The Genera of Araceae. Kew Bulletin 53. 505.
Crossref

   

Metcalfe CR (1960). Anatomy of monocotyledons. I. Gramineae. Claredon Press, Oxford.

   

Metcalfe CR, Chalk L (1979). Anatomy of Dicotyledons. (2nd edition)Vol. 1, Oxford University Press, New York.

   

Middendorf E (1982). The remarkable shooting idioblasts. Aroideana 6(1):9-11.

   

Mora M, Bernal R, Croat T, Jácome J (2006). A phytogeographic analysis of Araceae of Cabo Corrientes (Chocó, Colombia) and comparable lowland tropical American floras. Annals of Botany 93:359-366.
Crossref

   

Mudasiru OM, Ayodele AE, Akinloye AJ (2016). Taxonomic implication of wood characters in some members of the genus Terminalia Linn. (Combretaceae) in Nigeria. Nigerian Journal of Botany 29(1):23-41.

   

Mulligan GA, Munro DB (1990). Poisonous Plants of Canada. Ottawa, Canada.
Crossref

   

Ngoka DA (1997). Crop Production in the Tropics: Theory and Practice. Owerri Alphabeth Nigeria Publication P 170.

   

Okeke SE (1992). The correct nomenclature of the Nigerian species of Xanthosoma Schott (Araceae). Botanical Journal of the Linnean Society 110(3): 267-275.
Crossref

   

Okiy GEO (1960). Indigenous Nigerian Food Plants. Journal of the West African Science Association 6:117-121.

   

Oladipo OT, Oyaniran AO (2013). Taxonomic study of the wood anatomy of the genus Ocimum L. in Nigeria. Ife Journal of Science 15(2):95-302.

   

Onwueme IC (1978). The Tropical Tuber Crops. New York: Wiley.

   

Osuji JO (2006). Microstructural characters of the inflorescence bracts distinguish between Musa sapientum L. and M. paradisiaca L. International Journal of Botany 2(1):11-16.
Crossref

   

Osuji OJ, Nwala PC (2015). Epidermal and cytological studies on cultivars of Xanthosoma (L.) Schott and Colocasia (L.) Schott (Araceae). International Journal of Plant and Soil Science 4(2):149-155.
Crossref

   

Petruzzello M (2018). List of plants in the family Araceae. Encyclopædia Britannica. Encyclopædia Britannica, inc. Available at: https://www.britannica.com/topic/list-of-plants-in-the-family-Araceae-2075376

   

Purseglove JW (1972). Tropical Crops. Monocotyledons. Longmans Green, London. 1:70-74.

   

Rodriguez HG, Maiti R, Kumari A (2016). Research Advances on Leaf and Wood Anatomy of Woody Species of a Tamaulipan Thorn Scrub Forest and its Significance in Taxonomy and Drought Resistance. Forest Research 5:183.
Crossref

   

Solereder H (1908). Systematic anatomy of Dicotyledons. Vol. 2. Claredon Press, Oxford.

   

Solereder H, Meyer FJ (1928). Systematische Anatomie der Monokotyledonen. Principes - Synanthae - Spathiflorae Araceae. Gebruder Borntraeger, Berlin, p. 100-169.

   

Thair SS, Rajput MTM (2009). S.E.M. structure, distribution and taxonomic significance of foliar stomata in Sibbaldia L., species (Rosaceae). Pakistan Journal of Botany 41(5):2137-2143.

   

Thakuri HA, Patil DA (2011). Petiolar anatomy of some unstudied Euphorbiaceae. Journal of Phytological Research 2(12):54-59.

   

Vargas JH, Consiglio T, Jørgensen PM, Croat TB (2004). Modelling distribution patterns in a species-rich plant genus, Anthurium (Araceae), in Ecuador. Diversity Distribution10:211-216.
Crossref

   

 




          */?>