Isoetes × gopalkrishnae S.K.Singh, P.K.Shukla & N.K.Dubey

Singh, Sarvesh Kumar, Shukla, Santosh Kumar, Dubey, Nawal Kishore & Shukla, Pradeep Kumar, 2018, Isoetes × gopalkrishnae (Isoetaceae), a new interspecific sterile hybrid from central India, Phytotaxa 362 (1), pp. 68-76 : 71-74

Isoetes × gopalkrishnae S.K.Singh, P.K.Shukla & N.K.Dubey , hybr. nov. ( Figs. 1–2 )

( I. panchananii Pant & Srivastava × I. coromandelina Linnaeus )

Diagnosis:— Intermediate in morphology between Isoetes coromandelina and I. panchananii but it is distinguished from both putative parents and other Indian taxa by a combination of the following characters: absence of scales, leaf terete in transverse section, velum absent to rudimentary, megaspores with a coarsely rugulate surface ornamentation and a smooth equatorial girdle (band), microspores with densely echinate to shortly-cristate (echinae rounded, simple or branched) surface ornamentation.

Type:— INDIA. Uttar Pradesh: Vindhya plateau, Mirzapur district, Haliya, Ahugi Kala, 24°47’58.5” N, 82°17’22.3” E, 95.2 m, 21 November 2017, S. K. Singh, P. K. Shukla & S. K. Shukla SPKS 2117 (holotypus CAL! – N. B.: the holotype consists of a single plant).

Description:— Plants amphibious, emergent, tufted, deciduous, growing in margins of pond, 6–12 cm long. Rootstock corm globose, dark–brown, 6–10 mm wide, 3–9 mm high, deeply embedded in the soil, perennial, 2–lobed, each lobe 4–7 mm wide. Roots synchronously arising along the fossae, 3–5 unequal dichotomies in each root, older dark–brown, younger creamy–white, 15–35 mm long, 0.25–0.75 mm thick at base. Scales and phyllopodia absent. Leaves up to 21, nearly all sporophylls, simple, linear, spirally arranged, recurved to spreading, occasionally erect, yellowish–green distally when fresh or brownish–yellow when dry, uniformly 5–8.5 cm long, 4–8 mm wide at base, 4–5 mm wide above the sporangium, 1–1.5 mm wide at mid length, bases broadened, gradually tapering towards apex, apices attenuate, generally megasporangiate and rarely microsporangiate; alae hyaline, membranaceous, stretching along ca. 1/5 the length of the leaf, 0.25–0.5 mm wide above the sporangium, subula terate (rounded) in transversal section; interstellar canal 1; 4 longitudinal transversally septet air chambers with internal hairs; stomates present in upper 2/3 of the leaf, increasing in abundance distally. Peripheral fibrous bundles absent. Ligule present, triangular, delicate, margin straight, brownish–yellow, 2–2.5 mm long, 1.5–2 mm wide, generally not visible in dry material. Labium present, triangular with obtuse apex, yellowish–white, 1.5–2 mm long, 1–1.5 mm wide. Velum absent to rudimentary. Sporangia solitary, sessile, adaxial, embedded in basal cavity of leaf, basal, positioned 1–1.5 mm above the leaf base, elongated to obovate, adaxial surface flattened, black (megasporangia) to light brown (microsporangia); megasporangia 5–6 mm long, 3–3.5 mm wide at mid, contains 287–343 (331.11±6.57) megaspores; microsporangia 4.5–5.5 mm long, 3–3.5 mm wide at mid, containing numerous microspores; sporangial wall alike in both mega- and microsporangia, composed of two type of cell, long thread like and irregular shaped dark brown cells with internal pigments. Megaspores dimorphic. Larger megaspores trilete, rarely monolete, deltate to almost rounded, gray when wet or white when dry; 360–459 × 279–342 μm (monolete) 297–423 μm (trilete); distal hemisphere surface macrosculpture rugulate, rugulae sparse, rarely forming complete areole; proximal hemisphere surface macrosculpture pustulate each pyramic area with 1–5 pustules, pustules with or without coalescent bases and also with rugulae; laesures distinct, straight, 24–45 μm high, 36–54 μm wide, apex obtuse; equatorial girdle prominent and without rugulae, equatorial ridges thin and undulating, 32–48 μm high 27–45 μm wide, apex acute to obtuse. Smaller megaspores trilete, triangular, gray when wet or white when dry; 216–288 μm; distal hemisphere surface macrosculpture coarsely regulate with compact muri and not forming any areole like large megaspores; proximal hemisphere surface macrosculpture pustulate each pyramic area with 1–5 pustules or without pustules, pustules rarely with coalescent bases; laesures distinct, sinuous, 18–27 μm high, 18–27 μm wide, apex obtuse; equatorial girdle present, equatorial ridges thin and undulating, 13–18 μm high, 9–18 μm wide, apex acute. Microspores monolete, monomorphic, rounded to ovate, dark brown, 37–52 μm long, 27–38 μm wide, proximal ridge straight and wide, surface macrosculpture densely echinate to short-cristate, echinae rounded, simple and branched.

Etymology:— The specific epithet is given in the honour of Prof. Gopal Krishna Srivastava, Department of Botany, University of Allahabad, Allahabad, Uttar Pradesh, India. Prof. Srivastava, has contributed significantly to our understanding of the genus in India, described 8 new taxa (6 species and 2 variety) in the country.

Comments:— Six species of Isoetes with retate and reticulate megaspores have been described from different geographical areas of India: I. mahadevensis Srivastava, Pant & Shukla (1993: 106) , I. panchananii , I. panchganiensis Srivastava, Pant & Shukla (1993: 107) , I. rajasthanensis Gena & Bhardwaja (1984: 165) , I. reticulata Gena & Bhardwaja (1984: 166) and I. sampathkumarani Rao (1944: 287) . Table 1 compares salient features of all known Indian species with retate and reticulate megaspores and two other species ( I. coromandelina and I. indica ) with tuberculate megaspores found in close proximity and which share some characteristics with I. × gopalkrishnae . I. × gopalkrishnae is broadly similar to I. mahadevensis , I. panchananii , I. rajasthanensis , I. reticulata and I. sampathkumarani in the 2–lobed corm, absence of phyllopodia, length of the plant and leaves. The new hybrid is distinguished from other taxa by its absence of scales, leaf terete in transverse section, rugulate megaspore ornamentation and the presence of a plain equatorial girdle (also shared with I. panchganiensis ), microspores with densely echinate to shortly cristate ornamentation (echinae rounded and simple or branched), the velum being absent to rudimentary and a sporangial wall with internal pigmentation (also seen with I. panchananii ).

Distribution and Habitat:— Isoetes × gopalkrishnae is currently known only from a single spot of a pond at Ahugi Kala village near Haliya, Vindhya plateau, Uttar Pradesh. Plants are emergent in wet soil along the upper margin of the pond.

Phenology:— Plants were typically observed to develop in August, with spores maturing in late September and leaves disappearing in late November or early December (when water is drawn from the pond for agricultural irrigation purpose and it dries out).

Figures

FIGURE 1. Isoetes ×gopalkrishnae. A–C. Plants growing in habitat. C. Location of plants (Image taken from www.googlemap.com). D–E. Sporangial wall showing long thread like and irregular shaped dark brown cells with internal pigments. F–G. Megasporangia under SEM and LM. H. Transvers section of leaf shows terete (rounded) in outline, interstellar canal 1 and 4 longitudinal transversally septate air chambers.

FIGURE 2. Scanning electron microphotographs of Isoetes ×gopalkrishnae. A–D, I. Larger megaspore. E–F. Smaller megaspore. G–H, J. Microspore. A, E. Distal view of megaspores showing coarsely rugulate surface ornamentation. B. Distal view of megaspore showing coarsely rugulate surface ornamentation with presence of smooth equatorial girdle. C, F. Proximal view of trilete megaspore showing rugulae with pustules. D. Proximal view of monolete megaspore showing coarse rugulae with pustules. G. Microspores with distal and proximal view showing densely echinate to short-cristate surface ornamentation. H. Proximal view. I. Infrastructural details of megaspore. J. Infrastructural details of the surface of microspore showing echinae rounded, simple or branched.