Table 3 Comparative morphological characteristics of the studied RDS of family Apocynaceae used in ISM

A. curassavica

Slender, elongated, with several secondary and tertiary adventitious, fibrous roots

Samples smooth with no apparent wrinkles or furrows, greenish, root scars at some points. Few samples twisted with bends and secondary branches

Nearly circular in outline with a thin greenish-brown patch of cork zone followed by a comparatively light small zone. The primary central zone comprises a light brown woody part with numerous randomly distributed pores of very small size and several creamish rays emerging from the central region. A pith represents a small central hollow part

C. gigantea

Mostly thick roots with some comparatively thinner roots

Surface rough, light cream, with longitudinal fissures and transverse cracks. A powdery mass formed on the scrapping of bark

Nearly circular in outline, cork region light green, inner cortex region creamy pale. Central woody part nearly circular, pale with randomly scattered pores of varying size

C. procera

Mostly thick roots with some comparatively thinner roots

Surface rough, wrinkled, buff-colored, cylindrical, or irregular shaped. A powdery mass formed on the scrapping of bark

Irregular in outline, pale or light brown, thick bark protruded on sides, inner woody part pale having randomly scattered pores of varying size

C. carandas

Woody, hard, slender, less branched

Surface rough, dark brown with light patches in between. Bark with transverse cracks may be sloughed off from the woody part

Nearly circular in outline with the irregular outer surface, outer few patches light. Reddish-brown inner bark with less differentiation between cork and cortex, central woody part comprised of nearly uniformly distributed pores of varying size showing circular and spoke like arrangement. Bark may separate from the woody part

C. spinarum

Woody, hard, slender, and branched at some points

Surface light brown with wrinkles and nodule-like protuberances. A powdery mass formed on the scrapping of bark

Nearly circular with irregular bark outline. Bark light brown having several reddish-brown spots and a comparatively light central large woody region with several uniformly distributed pores of varying sizes

C. roseus

Varying thickness branched at some points with the light green surface

Surface light green, compact, and nearly smooth with no noticeable wrinkles or cracks

It may or may not be circular in outline. Outer surface corky and greenish, central part large, woody, pale with several small-sized evenly distributed pores traversed by spoke like rays

C. dubia

Elongated cylindrical, dark brown, branched at few points

Surface dark brown, wrinkled with several transverse cracks. Bark separated from the woody portion at several places

Cut root with sloughed off dark-colored scaly bark, inner cortex region creamish white, and central woody part with randomly scattered pores of varying size in the spoke-like arrangement. Some spoke like rays appear emerging from the center part

H. indicus

Elongated and of varying thickness

Surface rough, dark brown, or dark buff-colored, with transverse cracks. Bark separated from the woody portion at some places

Cut root surface irregular in outline with few small protrusions at some points, outer region thin, dark brown, maybe separated at few points from cortex part of main bark, cortex part light pale, central woody part appears nearly circular in outline with randomly scattered pores of varying size. Spoke-like rays emerging from the central part were also observed

H. pubescens

Cylindrical, thick, and long with few branches

Surface rough dark brown with numerous small longitudinal and transverse cracks

Circular in outline, the thin outer region is dark brown, inner light pale green zone with few small brown patches. Central woody part with small-sized pores of uniform distribution spoke like thin rays emerging from the central part. The root may show annular ring-like markings

I. frutescens

Dark brown woody pieces

Surface dark brown, rough with thick bark

Irregular in outline with a thin dark brown outer cork layer, inner cortex region thick with several small transversally flattened, dark brown, and reddish-brown patches. Central woody part irregular in outline with several uniformly distributed pores of varying size, arranged in a nearly circular pattern

M. tenacissima

Thick, cylindrical, less branched

Transversely cracked bark, surface deformed, appeared wrinkled with a nearly soft or smooth texture and buff-colored surface

Nearly circular in outline with outer thin, light green patches and inner large creamy white cortex zone with several golden-red spots. The central woody zone formed a comparatively small region than bark. Woody part relatively dark, comprised of several scattered pores of varying sizes

N. oleander

Elongated, thick with the dark brown surface

Less branched with brownish bark having small longitudinal fissures

Nearly circular or oval-shaped, bark thin with dark brown outer cork region, cortex region appears greenish-brown. Centre occupied by large woody part with a dilated center point having unevenly distributed small-sized pores of varying size

R. serpentina

Elongated, slender, thin, less branched, and irregular in shape

Surface rough and creamish pale. A powdery mass formed on the scrapping of bark

Irregular in outline with bark surface protuberances, outer cork region buff or light pale and inner cortex region formed a nearly circular, light cream band. The central part is the woody region with small-sized, uniformly distributed pores traversed by spoke-like rays emerging from the center (maybe dilated to one side)

T. divaricata

Long, slender, less branched, and of varying thickness

Surface buff-colored and rough, longitudinally wrinkled. Little powdery mass formed on scrapping of bark

Nearly circular in outline with greenish-brown bark region and large central pale woody region with uniformly distributed pores of varying size, and spoke like rays emerging from the center. The central part of the wood may appear dilated to one end