Xyloselinum laoticum Pimenov & Aver., 2016

Pimenov, Michael G., Degtjareva, Galina V., Ostroumova, Tatianaa., Samigullin, Tahir H. & Averyanov, Leonid V., 2016, Xyloselinum laoticum (Umbelliferae), a new species from Laos, and taxonomic placement of the genus in the light of nrDNA ITS sequence analysis, Phytotaxa 244 (3), pp. 248-262 : 252-259

Xyloselinum laoticum Pimenov & Aver. , sp. nov. ( Fig. 1–7 ).

Species nova e Xyloselino vietnamensi Pimenov & Kljuykov, qui proxima est, lobis terminalibus foliorum magis profunde incisis, subtus sine vesiculis, petiolis solidis (non fistulosis), petiolibus longioribus, umbellis umbellulisque ambitu sphaericis, radiis umbellarum subglabris (non pilis brevibus dense tectis), bracteolis lineatibus, edentatis, radiolis valde brevibus, fructibus 4.5–5.5 mm (non 7–7.5 mm) longis, stylopodiis conicis (non breveconicis) bene differt.

Type:— LAOS. Vientiane province: VangVieng district, Nam Pe village , about 12 km to the W of Vang Vieng town , around point 18°58’41.0”N, 102°18’54.1”E. Dry broad-leaved primary and secondary evergreen and semideciduous forest on very steep rocky slopes and on vertical cliffs of remnant highly eroded rocky limestone mountains composed of solid crystalline limestone at elevation 500–1000 m. Lithophytic undershrub to 1.5 m tall on rocky steep slope near mountain top. Very rare. 14 March 2013. N. T.Hiep, L.Averyanov, K.Chantthavongsa, N. S.Khang, P. V.The & S.Lopphengsy LA-VN 557 (holotype: LE, Fig. 2 ; isotypes: CPC Herbarium, HNL, FOF) .

Subshrub, deciduous, 0.5–1.5 m tall. Stems solitary, woody in lower part, 3–4 cm in diam., round in cross-section, finely ribbed. Leaves 2- or 3-pinnatisect, glabrous; sheaths narrow triangular, amplexicaul, ribbed; petioles solid, 3–8 cm long; leaf blades broadly triangular in outline, 20–26 × 15–18 cm; primary and secondary segments petiolulate, petiolules of basal segments up to 5 cm long; terminal segments ovate to broadly lanceolate, 4–7 × 1.5–3.5 cm, truncate to slightly attenuate at apex, irregularly toothed along the margin or sometimes laciniate, with prominent central veins and without bladders on lower surface. Synflorescence branched, loosely divaricate; umbels with peduncles 3–6 cm long, globose, 5.5–9 cm in diam.; rays 12–15, subequal, rigid, thin ribbed, almost glabrous; bracts absent. Umbelets globose, 1.4–2 cm in diam. (without fruits), with several short (considerably shorter than umbellet rays), linear, entire bracteoles; pedicels 10–18 subequal, rigid divaricate, covered with short prickles.Calyx teeth short, triangular, persistent in fruits. Petals unknown. Fruits ( Figs. 5–7 ) with carpophore bipartite at the base. Mericarps dorsally compressed, 4.5– 5.5 x ca. 4 mm, ovate in outline, slightly convex at dorsal side; dorsal ribs low keeled, marginal ribs narrowly winged; stylopods conical; styles short, slightly flattened, reflexed. Exocarp of small cells, interrupts near the end of marginal ribs (commissure broad). Mesocarp partly parenchymatous, partly sclerenchymatous (whole commissural side and between secretory ducts on dorsal side). Parenchyma of marginal ribs consisting of cells with pitted slightly lignified walls. Vittae rather large, solitary between dorsal ribs, 2 or 3 between dorsal and marginal ribs, 6 on commissural side. Rib secretory ducts inconspicuous. Endocarp and seed coat in mature fruits destroyed. Endosperm on commissural side flat, on dorsal side sulcate under vittae.

Phenology:—The type specimen with mature fruits was collected in March. The paratype specimen with young green leaves and no fruits was collected approximately at the same time in similar habitat but at a much higher elevation.

Diagnostic characters:— Similar to two previously described species, X. laoticum is subshrubby plant with 2–3- pinnatisect leaves having petiolulate basal segments and broadly lanceolate terminal segments, mericarp vallecular vittae solitary or binary, endosperm almost flat on the commissural side. It is more closely related to X. vietnamense than X. leonidii . Xyloselinum laoticum differs from X. vietnamense in irregularly toothed or sometimes laciniate terminal leaf segments without bladders on lower surface, solid (not fistulose) petioles,globose umbels and umbellets, almost glabrous (not densely covered by scattered short prickles umbel rays, entire bracteoles, and conical (not shortly conical) stylopods. X. laoticum differs from X. leonidii in terminal leaf segments lanceolate, 4–7 cm long, irregularly toothed or laciniate (not deeply lobed, 1.5–2.5 cm long), globose umbels and umbellets, umbel rays 12–15 (not 20–25), entire bracteoles, carpophore bipartite at the base (not reduced), pedicels 10–18, covered with short prickles (not 20–22, glabrous), mericarps 4.5–5.5 x 4 mm, with narrow winged marginal ribs (not 6.5–6.7 x 2.8–3 mm, with broadly winged marginal ribs).

Distribution and habitat:—The species is known only from Vientiane province of Lao PDR, where it grows in rather dry primary and secondary broad-leaved evergreen and semi-deciduous forests on very steep rocky slopes and on vertical cliffs at the tops of highly eroded rocky mountains composed of solid crystalline limestone at an elevations of 500–1750 m ( Fig. 1 ).

Etymology:—The specific epithet refers to the geographical origin of the species.

Additional specimen examined (paratypes):— LAOS. Vientiane Province: Kasi District, Namken village, Phachao Mt., around point 19°18’45.5”N, 102°22’31.4”E, primary broad-leaf evergreen forest on very steep rocky slopes of remnant mountain composed of highly eroded solid crystalline limestone at elevations 1500–1750 m. Lithophytic undershrub 0.5–0.8 m tall with woody stem 3–4 cm in diam on exposed rocks on mountain top. Very common. 24 March 2013, L. Averyanov, N.S. Khang & S. Lorphengsy LA-VN 778 (CPC Herbarium, LE, NHL, FOF).

Molecular data: —Maximum parsimony analyses recovered 61,960 shortest trees with 1,075 steps (CI = 0.4753, RI = 0.7856). The Bayesian tree is consistent with the most parsimonious trees, but it seemed resolve the relationships between different clades better than the parsimony analysis, where many of the groups demonstrated large polytomy. Thus, only the Bayesian 50% majority rule tree with posterior probabilities values (PP) and parsimony bootstrap percentage (BS) is shown in Fig. 8 . In both, maximum parsimony and Bayesian trees our new species belongs to a clade with the other species of Xyloselinum , X. leonidii , and this grouping is strongly supported (PP 1; BS 99%). The third Xyloselinum species, X. vietnamense , was not included in analysis. A Bayesian tree indicates differences in the ITS sequence among two Xyloselinum species.

Figures

FIGURE 1. Xyloselinum laoticum in natural habitats (paratype—LA-VN 778). A. Habitat. B, C. Mature plants, view from above. D, E. Mature plants, side view. F. Young leaves. G. Leaves at apical rosette [All photos of N.S. Khang, image correction and design by L. Averyanov].

FIGURE 2. Photograph of holotype specimen of Xyloselinum laoticum (LA-VN 557).

FIGURE 3. Photograph of paratype specimen of Xyloselinum laoticum (LA-VN 778).

FIGURE 4. Photograph of paratype specimen of Xyloselinum laoticum (LA-VN 778).

FIGURE 5. Mericarps of Xyloselinum laoticum. A. dorsal view with calyx teeth (arrowheads), B. commissural view. Scale bar = 1 mm.

FIGURE 6. Mericarp transection in Xyloselinum laoticum, schematic. Abbreviations: dc—commissural secretory ducts, dv—vallecular secretory ducts, en—endosperm, ex—exocarp, lp—lignified parenchyma with pitted walls, sc—sclerenchyma, vb—vascular bundle. Scale bar = 1 mm.

FIGURE 7. Fruit anatomical details in Xyloselinum laoticum. A. median rib with vascular bundle (arrow) and vallecular secretory duct; B. lateral vallecula with secretory ducts and sclerenchyma layer (arrow) between them; C. the middle part of commissura with funicular bundle (short arrow) and sclerenchymatic pericarp (long arrow); D. distal part of marginal rib with vascular bundle (arowhead), pitted lignified parenchyma (long arrow), exocarp border (short arrow); E. commissural secretory ducts and sclerenchyma layer (arrow) between them. Scale bar = 0.1 mm.

FIGURE 8. The Bayesian tree obtained from analysis of 86 nrITS sequences. Branch lengths are proportional to the number of character changes. Maximum parsimony bootstrap support and Bayesian posterior probabilities are indicated above nodes. Branches that collapse in the strict consensus tree are shown as dashed lines. The names of main clades recognized in currently adopted molecular phylogeny of Umbelliferae (Downie et al. 2010) as well as Peucedanum s.str. group are indicated. Xyloselinum species are shown in bold.