Keywords

Introduction

The family Moraceae comprises of 37 genera and 1050 species (Berg et al. 2006) and has mostly trees or shrubs. It is widely distributed in tropical and sub-tropical regions of the world and a few in temperate regions (Raturi et al. 2001). It consists of five tribes namely Moreae, Artocarpeae, Dorstenieae, Castilleae and Ficeae (Berg 2001). Of these, Artocarpeae also known as breadfruit tribe, is characterised by inflorescence architecture (simple spike to complex globose heads), reduction of stamen number, peltate interfloral bracts, vitreous silica and straight filaments. Artocarpus, Hullettia, Paratocarpus, Prainea, Batocarpus and Clarisia are important genera of this tribe (Datwyler and Weiblen 2004; Clement and Weiblen 2009). Artocarpus J.R. Forst. is the largest genus in the tribe and third largest genus in the family Moraceae after Ficus and Dorstenia. It has about 45 species which are distributed in Indo-Malayan region of South-East Asia and about 7–8 species are known to occur in India (Raturi et al. 2001).

A limited information is available on anatomical studies of Artocarpus (Gamble 1922; Purkayastha 1996). Topper and Koek Noorman (1980) reported presence of laticifers in ray tissue and fibre tissue in number of Artocarpus species, while Anoop et al. (2011) carried out study on variation in bark thickness, heartwood content, fibre morphology, vessel and ray morphology in A. heterophyllus Lam. and A. hirsutus to understand radial variation in wood anatomical properties within trees. Raturi et al. (2001) described the gross structure of A. chama, A. gomezianus, A. heterophyllus, A. hirsutus and A. lakoocha collected from other parts of India, Bangladesh and Myanmar. There is no report on anatomy of A. nitidus in the available literature. The present study is an attempt to describe the wood anatomy of four species of Artocarpus of NE India with an aim to evaluate variation in anatomical characteristics within and among species both qualitatively and quantitatively.

Materials and Methods

The samples of A. chaplasha Roxb., A. heterophyllus Lam., A. lakoocha Roxb. and A. nitidus Trec. were collected from forests of Assam and Mizoram as listed in Table 1. Eight trees with straight bole and uniform crown were selected for each species, and wood samples of size 5 cm3 were taken at breast height. Each wooden block was cut into 2 cm3 size and fixed in FAA for 24–48 h, after which they were preserved in 50% alcohol. Cross, radial longitudinal and tangential longitudinal sections were cut with the help of a sliding microtome. Permanent slides were prepared by following standard procedure. Small radial slivers of different Artocarpus species were treated with Franklin’s solution for maceration to measure fibre and vessel length. Temporary slides were prepared by using 50% glycerol, and a random sample of 50 fibres and 50 vessels were measured from each sample with the help of an ocular micrometre at 40×. Twenty-five counts were taken for parameters like vessel diameter, fibre diameter, fibre wall thickness, ray height, and ray width, and 10 fields were selected on cross section to determine tissue proportion, vessel frequency and number of rays per mm. The data was analysed by software SPSS 16 and Microsoft excel 2007. The terminology and measurements were taken according to IAWA Committee (1989). Wood specific gravity was determined by water displacement method.

Table 1 List of selected Artocarpus species
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Results and Discussion

Growth ring boundaries indistinct with diffuse porous wood. Vessels circular or oval in outline, solitary or in radial multiple of 2–3, simple perforation plate, intervessel pits alternate and vessel ray pits similar to intervessel pits in size and shape (Fig. 1a–e). Quantitative anatomical features are summarised in Table 2. Mean vessel length, vessel diameter and vessel frequency vary from 284.4 ± 82.61 µm (A. nitidus) to 350.5 ± 102.75 µm (A. chaplasha), 213 ± 76.80 µm (A. chaplasha) to 277.92 ± 93.82 µm (A. nitidus). Range of vessel frequency is 4–5 per mm2 (Table 2). Vessel percentage varies from 12% (A. nitidus) to 26% (A. heterophyllus) (Fig. 2).

Fig. 1
figure 1

a–e Cross sections: diffuse-porous wood; vessels mostly solitary and in radial multiple of 2 in A. chaplasha (a) and A. nitidus (e); lozenge aliform and confluent parenchyma in A. chaplasha (a, b); lozenge aliform and vasicentric parenchyma in A. heterophyllus (c); lozenge aliform parenchyma in A. lakoocha and A. nitidus (d, e); ray flecks in A. chaplasha (b). f–j Tangential longitudinal sections: Biseriate, multiseriate rays and radial latex ducts in A. chaplasha (f, g); multiseriate rays and parenchyma strand in A. heterophyllus (h); multiseriate rays and sheath cells in A. lakoocha and A. nitidus (i, j). k–n Radial longitudinal sections: heterocellular rays comprising of body ray cells procumbent with marginal rows of square/upright cells in A. chaplasha (k), A. lakoocha and A. nitidus (m, n); homocellular rays comprising of procumbent cells in A. heterophyllus (l); laticifers in the form of dark streaks present among fibres in A. lakoocha (m) and in square/upright cells in A. nitidus (n)

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Table 2 Dimensions of xylem elements in Artocarpus species
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Fig. 2
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Tissue proportion of selected species of Artocarpus

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Fibres are square or polygonal in outline and constitute the ground tissue. Mean fibre length, fibre diameter and fibre wall thickness range from 1193.73 ± 326.71 µm (A. heterophyllus) to 1425.0 ± 338.70 µm (A. lakoocha), 165.57 ± 70.11 µm (A. nitidus) to 209.3 ± 59.92 µm (A. chaplasha) and 3.21 ± 2.34 µm (A. heterophyllus) to 4.90 ± 2.43 µm (A. nitidus) respectively. Septate fibres present except in A. heterophyllus. Fibre percentage varies from 44% (A. chaplasha) to 50% (A. lakoocha) (Fig. 2). Laticifers in the form of black streaks present among fibres in A. heterophyllus and A. nitidus (Fig. 1n).

Lozenge aliform parenchyma is present in all selected species. In addition, vasicentric parenchyma in A. lakoocha and A. heterophyllus and confluent parenchyma in A. chaplasha and A. lakoocha are observed (Fig. 1a, d). Parenchyma strands are 2–4 celled. Parenchyma percentage varies from 13% (A. chaplasha) to 21% (A. lakoocha) (Fig. 2).

Rays are uniseriate, biseriate and multiseriate in all species (Fig. 1f–j). Rays are heterocellular and composed of procumbent body cells with mostly two rows of upright/square marginal cells. Homocellular rays are recorded in few samples of A. heterophyllus (Fig. 2k–n). Ray height and ray width vary from 496.83 ± 171.75 µm to 58.87 ± 14.04 µm (A. chaplasha) to 599.08 ± 144.02 µm and 70.99 ± 13.23 µm (A. nitidus) respectively. Rays per mm are 4 (A. chaplasha) to 6 (A. heterophyllus). Rays percentage is recorded 15% in A. chaplasha and A. heterophyllus, while A. lakoocha and A. nitidus show 17%. Ray flecks and radial latex ducts in rays of A. chaplasha (Fig. 1b, g), sheath cells in rays of A. lakoocha and A. nitidus (Fig. 1j) are recorded. Also laticifers in the form of black streaks are recorded in square/upright cells of A. lakoocha.

The present study shows that the wood of all selected species have common qualitative characters like indistinct growth rings, diffuse-porous wood, solitary vessel, simple perforation plate, vessel ray pitting, heterocellular ray and lozenge aliform parenchyma. These features are in agreement with the findings of Raturi et al. (2001) and Purkayastha (1996). Since these features are present in all species, therefore, these can be considered as characteristics of genus Artocarpus. Despite these, other features like presence of vasicentric parenchyma in A. lakoocha and A. heterophyllus, confluent parenchyma in A. chaplasha and A. lakoocha, absence of septate fibres in A. heterophyllus, radial latex ducts and ray flecks in A. chaplasha, sheath cells in A. lakoocha and A. nitidus have been reported first time and can be used to differentiate these four species. Ray flecks were observed in few samples of A. chaplasha. The formation of ray flecks may be attributed to localised injury of cambium (Carlquist 2001) and was also reported by Purkayastha (1996) in the same species. Topper and Koek-Noorman (1980) reported radial latex ducts in A. lakoocha and A. nitidus. On the other hand, the laticifers in the form of dark streaks among fibres in A. heterophyllus and A. nitidus and radial latex ducts only in A. chaplasha are reported in the present study.

Analysis of variance was carried out in quantitative anatomical characters to see the variation within and among species. The results, presented in Table 3, indicate statistically non-significant differences within species and statistically significant differences among species. It indicates that selected wood element dimensions do not have any variation within species. But Artocarpus species can be differentiated on the basis of significant quantitative variation in wood element dimensions.

Table 3 Analysis of variance for selected parameters among selected species of Artocarpus
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Correlation among different dimensions of wood elements and their relationship with specific gravity is presented in Table 4. The relationship among most of the parameters was too weak to be significant. Fibre length exhibited positive and significant correlation with fibre diameter and vessel length. Specific gravity was positively and significantly correlated with ray width, but negatively and significantly correlated with fibre diameter. It indicates that most of the anatomical parameters do not influence each other, but some fibre characteristics affect specific gravity. The present results corroborate the findings of other workers (Pande et al. 2005; Sharma et al. 2011a, b, 2014; Singh et al. 2013) in other hardwood species.

Table 4 Pearson correlation among parameters of wood elements among selected species of Artocarpus
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Key for identification of Artocarpus species is given below:

  1. 1.

    Heterocellular rays and septate fibre present—————2

    Heterocellular rays and septate fibre absent—————A. heterophyllus

  2. 2.

    Laticifers in the form of dark streaks among fibres present—————A. nitidus

    Laticifers in the form of dark streaks among fibres absent—————3

  3. 3.

    Sheath cells present, both ray flecks and radial latex duct absent—————A. lakoocha

    Sheath cells present, both ray flecks and radial latex duct present—————A. chaplasha.

Conclusions

All the Artocarpus species have common features like diffuse-porous wood, vessel solitary or in radial multiple of 2–3, simple perforation plate, alternate intervessel pits, vessel ray pits similar to intervessel pits in shape and size, heterocellular ray and lozenge aliform parenchyma. Septate fibres are present in all selected species except A. heterophyllus. Ray flecks and radial latex ducts are present only in A. chaplasha, while, in other species, laticifers in the form of black streaks among fibres (A. heterophyllus and A. nitidus) and in upright/square cells of rays (A. lakoocha) are present. Quantitative anatomical characters like fibre length, fibre diameter, fibre wall thickness, vessel length, vessel diameter, ray height, ray width show statistically non-significant variation within species and statistically significant variation among species. Wood specific gravity is positively and significantly correlated with ray width. Identification key is prepared on the basis of qualitative anatomical features for separation of species.