Ischaemum dioecum Landge & R. D. Shinde, 2022

Landge, Shahid Nawaz & Shinde, Rajendra D., 2022, Ischaemum dioecum (Poaceae: Andropogoneae): the most strangest new species from Northern Western Ghats, Maharashtra, India, Phytotaxa 533 (5), pp. 237-255 : 239-242

Ischaemum dioecum Landge & R. D. Shinde , sp. nov. ( Figs. 1 , 2 & 3 )

Type:— INDIA. Maharashtra state: Raigad district, near Patanus village , 8 August 2021, 18°26’51.7”N 73°22’17.1”E, Shahid Nawaz PR-01 A ( BLAT) [holotype]; isotype: Shahid Nawaz PR-01 B ( BLAT) [pistillate plant specimens] .

Diagnosis:—Ephemeral habit, up to 20 cm high, with numerous stilt-roots from nodes; dioecious breeding system; leaves long, hispid, acute at the base and petioled; lower glume of the sessile and pedicelled spikelet (if present) 2–4- nerved; lower floret in the sessile spikelet absent or if present then barren, elodiculate and epaleate; upper floret of the staminate plant is lodiculate (lodicules giant, ca. 3.5 mm long) bearing four stamens with anthers 6.0– 10 mm long on an extremely filiform and extraordinarily elongated filaments ca. 15 mm long; upper floret of the pistillate plant is elodiculate with unusually long style ca. 14 mm long with two plumose stigma, purplish, 6.0–10 (–14) m long; peduncle in staminate plant glandular beset with tubercle-based trichomes; palea apex bi-dentate most often with a central arista; pedicelled spikelet (if present) half as long as the sessile spikelet, barren, reduced to a single glume; pedicel 1/2–4/5 of the sessile spikelet, slender, linear glabrous or ciliate on the margin.

Description:—Male plant: Ephemeral, ca. 20 cm, geniculately ascending, non-caespitose, extremely delicate, weak and slender with numerous maroonish-red stilt-roots (roots very delicate and may easily break) from the nodes bearing micro papillae near the base. Leaf blade linear, acuminate, very thin membranous, hispid, 2.0–5.0 × 0.3– 0.5 cm, acute at the base with a long pseudopetiole (ca. 1.5 cm long), puberulous. Ligule ca. 3.0–4.0 mm long, oblong-lanceolate, membranous, lacerated at the apex into few segments, hairy on the margin or not. Sheath very slender, terete, striated, glabrous, margin sub-hyaline-membranous strongly overlapping, 1.0– 3.5 cm long, not keeled. Inflorescence a solitary spiciform-raceme fully exserted from the spathaceous sheath. Peduncle broad, somewhat swollen bearing tubercle-based bristles, elongated, with glandular depressions oozing a dense brownish viscous fluid. Spiciform-raceme ca. 28–42 mm long, solitary, comprising three well developed sessile spikelets with bare pedicels (on maturity deciduous together with the adjacent rhachis internode and pedicel) pedicelled spikelets are sometimes present but by a single, reduced glume. Sessile spikelet: linear-oblong, awnless, 9.0–12 (–13) mm long (including a callus); callus, ca. 1.2–2.2 mm long, densely bearded with white hairs (i.e. 6.0–9.0 mm long), reaching up to the middle of the sessile spikelet; lower glume: linear-oblong, 8.0–10 (–13) × 2.0–3.0 (3.5) mm, slightly longer than the upper glume, convex base wards and flattened upwards, initially herbaceous-membranous and later becoming somewhat coriaceous, scabrous, puberulous or glabrous, apex acute, 2–4-nerved (only 2 clearly visible other two obscure), nerves not anastomosing, margin evenly inflexed throughout the length, sharply keeled upwards, glabrous, no trace of nodulations and rugosity; upper glume: linear-lanceolate, 7.0–9.0 (–12) × 2.2–3.3 (–3.8) mm, 1–3-nerved, glabrous, acute, naviculate, keeled, slightly winged near the apex, ciliate, margins inflexed. Floret: lower floret is absent only upper floret is present, staminate: lemma linear-lanceolate, almost equal to upper glume in length but narrower, 3-nerved, glabrous, hyaline-membranous, acute, un-awned; palea linear long obspatulate, sub-equal to its lemma, broadest at the base, hyaline-membranous, 3-nerved, apex bi-dentate (often with a distinct arista from the sinus (excurrent mid-nerve), arista ca. 3.0– 4.5 mm long), glabrous. Pedicelled spikelet: Absent most of the times, if present then by a single 2-nerved reduced glume ca. 5.0 mm long. Pedicel linear, slender, 7.0– 10 mm long, ciliate on both the angles or completely glabrous. Rhachis internode sub-equal to the pedicel and almost identical in shape, ciliate on both the angles or completely glabrous, fragile and articulate. Stamens four, filaments slender, drooping, considerably elongated during anthesis reaching ca. 15 mm long; anthers 6.0– 10 mm long, orangish-yellow, exhibiting both lateral and apical dehiscence. Lodicules fleshy, sub-hyaline, clavate, sharply oblique at the apex, ca. 3.5 mm long. Pedicelled spikelets short almost reduced to a glume, barren or absent altogether. Female plant: An extremely slender, delicate, geniculately ascending, stilt-rooted, non-caespitose ephemeral grass, 10–14 cm high. Culm solitary, weak, un-branched, striated, up to 12-noded, hardly exceeding 0.6 mm diameter; the root system is extremely shallow; internodes as long as the sheath or slightly longer, terete; nodes swollen, glabrous, some lower and few upper ones with stilt roots up to about half the length of the plant. Sheaths 0.8–2.5 cm long, terete, glabrous or setaceous near the margin with bulbousbased trichomes (ca. 3.0 mm long), tightly en-clasping and disintegrating in the lower portion of the culm during anthesis, sheath near the inflorescence is quite broad, somewhat ribbed, slipping-off and slightly laterally compressed. Ligule membranous, ca. 1.0 mm long, slightly brownish, obtuse to somewhat truncate at the apex with appressed white hairs on the adaxial side. Blade: lower linear-lanceolate longer than the upper ones, 0.8–2.0 × 0.2–0.3 cm, the ones about the inflorescence are ovate-elliptic to slightly oblongish in outline, beset with bulbous-based trichomes (1.0– 1.5 mm long) on both the surfaces, margins uniseriately-pectinate. Inflorescence a highly reduced, solitary (with a triad of one sessile spikelet and two bare pedicels, sometimes with a single glume) or binate (each spiciform-raceme is reduced to only single sessile spikelet accompanied by a barren pedicel) spiciform-raceme, 5.0– 5.6 mm long, almost completely subtended by a spathaceous sheath; fragile on maturity and sessile spikelets deciduous together with the adjacent rhachis internode and pedicel. Peduncle very short, slender, clavate, glabrous, rarely more than 10 mm long, apex dilated and broad. Spikelets either sessile or in a combination of one sessile and other pedicelled (often reduced to a single, barren glume) in a raceme. Sessile spikelet: ovate-lanceolate, 5.0– 5.6 mm long (including a callus), strictly pistillate; callus 0.8–1.0 mm long, slightly oblique, broad, bearded with white hairs almost reaching the middle of the sessile spikelet; lower glume: ovate-lanceolate, 5.0–5.6 × 1.5–1.8 mm (un-opened, broadest near the base), slightly shorter than the upper glume, initially herbaceous-membranous and later becoming somewhat coriaceous, convex towards the base with two bosses and flattened upwards (sometimes with two shallow bosses in the middle and below), glabrous or hairy on the back, apex acute to somewhat bi-dentate with a short hyaline portion, 2–4-nerved (only two clearly visible others obscure), nerves not anastomosing, margins glabrous, broadly and evenly inflexed throughout the length, keels acute, no trace of nodulations and rugosity; upper glume: ovate-lanceolate, 5.1–5.7 × 1.5–1.8 mm (broadest at the base), navicular, keel herbaceous, 3-nerved, glabrous, sub-hylaine, apex acute, devoid of a hump in the middle, margin hyaline, glabrous and inflexed; lower floret: entirely absent (if present then barren and is only represented by an epaleate lemma which is ovate-lanceolate, 3.2 mm long (broadest near the base), barren, without lodicules, glabrous, hyaline-membranous, 1–3-nerved, apex obtuse or slightly oblique); upper floret: strictly female/ pistillate, elodiculate: upper lemma linear-lanceolate, 4.0–5.4 × 0.8–1.0 mm, sub-equal to lower glume, paleate, bi-fid (lobes acuminate, 1.8–2.5 mm long), glabrous, awn geniculate issuing from the sinus, 12.5 mm long (column brown 5.0 mm long and bristle pale, scabrid, 7.5 mm long), slightly humped in the middle on the dorsal side; upper palea: very linear, almost obspatulate with a broad base (enclosing an ovary) and linear upper portion, 3.0–4.0 × 0.3–0.4 mm (broadest at the base), very delicate, hyaline-membranous, margin inflexed, broader at the base, glabrous, apex bidentate (often shortly mucronate from the sinus (excurrent mid-nerve), mucro ca. 1.0–2.0 mm long), finely 3-nerved; pistil: ovary ovoid, 1.0 mm long, style ca. 14 mm long (when young, highly coiled inside the spikelet), two stigma plumose, purplish, 6.0–10 (–14) mm long; lodicules absent; caryopsis not seen. Pedicelled spikelet: represented only by a bare pedicel, which is extremely narrow, not swollen, linear, 3.2–4.0 × 0.2–0.3 mm, unusually long, flattened, excavated throughout on the inner angle, confluent into the callus, hairy along the margins or completely glabrous, apex densely bearded or with a calloid outgrowth, mostly devoid of pedicelled spikelet sometimes with a single lower glume (un-identical to the lower glume of sessile spikelet, linear-elliptic 3.2 mm long, 2–4-nerved (only two are clearly visible), sub-hyaline, herbaceous, convex on the back and apex bi-dentate).

Distribution:—Hitherto, based on our surveys, the species has been observed only in a couple of localities i.e. near Patanus village and Rawalje village, Raigad District, Maharashtra (Western Ghats), India. Ischaemum dioecum is apparently an extremely rare and narrow endemic species in the genus.

Flowering and fruiting:—August to mid September (life cycle of individuals hardly exceeding 20 days).

Additional specimen examined:— INDIA. Maharashtra state: Raigad district, near Rawalje village , 24 August 2021, 18°26’36.9”N 73°21’29.0”E, Shahid Nawaz RR-05 ( BLAT) [staminate plant specimen, spikelets were removed for the study] .

Habitats and ecology:—In complex network of dense roots mingled with seasonally wet thin film of soil at the base of other taller grass species such as: Ischaemum diplopogon Hooker (1896: 129) , Heteropogon ritchiei & Dimeria blatteri Bor (1949: 70) , on the flank of the river associated with rocky outcrops and on the slope of basalt rocks. The microhabitats are protected from the direct sunlight, wind and precipitation; thus are special with their own specific environmental conditions that include moisture, temperature and light. These factors are regulated by the presence of benefactor species (three mentioned above) from directly influencing I. dioecum therefore contributing positively in survival of this species. In the late October, when monsoon subsides, the resultant heat generated by the basalt rocks, on prolonged exposure to sunlight is immense; eradicating all the annual and transient vegetation cover. In such challenging habitats, plants that are acclimatized rapidly complete their life cycle by bearing seeds. In which I. dioecum has the shortest life cycle, hardly exceeding 20 days!

Associated species:— Arundinella pumila Steudel (1854: 114) , Heteropogon ritchiei , Ischaemum diplopogon , Dimeria blatteri , Ischaemum barbatum Retzius (1791: 35) , I. semisagittatum Roxburgh (1832: 320) , Ischaemum sp. , Geissaspis sp.

Etymology:—The epithet alludes to a dioecious breeding system of the species, where male and female plants are sexually separate individuals.

Population and threat:—In the first locality the habitats are encroached and disturbed by tourists visiting Devkund waterfall during monsoon when the individuals are in flowering. The first author has also observed that the shallow shores of the river attract many villagers especially women for washing clothes. However, the second locality is far from the reach, at least for villagers and their livestock. The basalt slopes make the domestic quadrupeds unable to climb and disturb the thin population of Ischaemum dioecum . These basalt habitats, during monsoon, are extremely slippery and difficult to climb upon. At least because of this, there the population of this extremely rare grass is, perhaps, on a small magnitude, protected. However, in this habitats Celosia sp. is very troublesome and exhibits a great possession. It may threat the existence of this species in future.

IUCN status:—Based on our field observations, it can be asserted that the population is severely fragmented and confined over the two localities ( Figs. 3 & 4 ) few kilometers apart from each other. The type locality exhibits tourist encroachment and disturbance. The total number of individuals in both the subpopulations is less than 25 in which female plants are relatively higher in numbers as compared to the male counterparts. The observed data suggests 7 male individuals over 18 female individuals. Hitherto, based on the limited surveys, data is not available to discuss declination thus those categories and criteria cannot be assessed. We have not seen Ischaemum dioecum in any other locality except the two given though surveyed the region more or less for almost a month during monsoon. Based on this it is perhaps not too quick to assess the plant as Critically Endangered (CR) under B1 (Extent of occurrence <100 km 2), D (mature individuals <50) of IUCN Red List Categories and Criteria (2019).

Notes:—Since, the species is extremely delicate, slender, weak and non-tufted, it demands an additional support from the stilt-roots, that are present up to almost half of the plant height assisting it to stand upright without falling. In some specimens stilt-roots are present till the last node i.e. below the inflorescence, and may measure up to 12 cm high. The staminate and pistillate plants differed quite sufficiently in appearance of the inflorescence that one might easily mistake them for members of different species! The most striking contrast between the two is that the formers are essentially awnless, whilst those of the pistillate plants bear conspicuous awns ( Figs. 1 & 2 ). The features that are common in both plants are such as: solitary habit with stilt-roots; leaves thin-membranous, hispid, long, petioled and acute at the base; ligule membranous; few spikelets up to three or less than three in the spiciform-raceme; 2–4-nerved lower glumes of the sessile spikelets; lower floret absent; upper palea bi-dentate at the apex with an arista from the sinus and pedicelled spikelets absent or reduced to a single glume i.e. half the length of the sessile spikelets.

Females in comparison to males are, at least somewhat, easier to search in the field and tend to exist in a relatively higher numbers. Whilst, the male plants are very few and extremely rare in occurrence and challenging to trace; so far, we, during our surveys, found only few male plants in which only two were collected for further study. As compared to the female plants, males are slightly taller, more delicate, bearing thinner leaves and higher number of stilt-roots.

Figures

FIGURE 1. Ischaemum dioecum. A. Habit. B. Magnified upper portion of the plant with raceme. C. Magnified raceme showing the apically exserted stigma (stigma highly broken). D. Spikelets with a subtending sheath. E. Pistil from the young spikelet. (Based on Shahid Nawaz PR-01B at BLAT: isotype). F. Male plant (un-awned) from second locality [Shahid Nawaz RR-05; paratype]. G. Female plant (awned) from the first locality [Shahid Nawaz PR-01A; holotype]. (Photography by: Shahid Nawaz)

FIGURE 2. Illustration of Ischaemum dioecum (The male plant and its parts have been redrawn from the field note book of Shahid Nawaz). A–C & H–S: Male plant & its parts. D–G: Female plant and its parts. A. Male plant habit. B. Magnified peduncle. C. Sessile spikelet opened-up. D. Female plant habit. E1. Reduced bi-nate spiciform-raceme (sheath and callus hairs were removed to expose the raceme). E2. Pistil from the mature spikelet. F. Lower glume (outer view). G. Lower glume (lateral view). H. Sessile spikelet. I. Lower glume (outer view). J. Lower glume (inner view). K. Lower glume (lateral view). L. Upper glume (inner view). M. Upper glume (lateral view). N. Lemma. O. Palea. P. Stamens. Q. Lodicules. R. Rhachis internode and pedicel. S. Pedicelled spikelet. (Illustrated by: Shahid Nawaz) Note: Male plants, as compared to their female counterparts, were quite fewer and extremely delicate. Thus, the first author dissected and studied a couple of fresh specimens on the field under a dissecting microscope and illustrated the floral parts in his field notebook. Later, after facing an irreversible loss of the intended type specimens of the male plant of Ischaemum dioecum with other important grass specimens in the field, his field note book was reconsidered to redraw and reproduce the same illustration for this paper. A re-visit to the type locality at the end of October 2021, when monsoon had subsided, revealed that the previously associated other grasses had now established a gregarious community possessing a taller stature, and the very effort to examine their roots and bases was futile. Sooner, the thin population of I. dioecum had completely disappeared. In view of the very restricted range of this species, it perhaps seems that, it has not been very successful in colonization and may be very recent in origin. It is also reflected through its acquisition of such a unique microclimatic condition to live that in absence of which the species might become extinct.

FIGURE 3. Transient microhabitats of Ischaemum dioecum in the type locality during monsoon (first locality: near Patanus village) (Alphabets M & F followed by arrows indicate male and female plants respectively). (Photography by: Shahid Nawaz)

FIGURE 4. Transient microhabitats of Ischaemum dioecum on the soil-filled cracks of basalt slope in post monsoon period (second locality: near Rawalje village). (Photography by: Shahid Nawaz)