Dendrothrix condorensis K.Wurdack, 2017

Wurdack, Kenneth J., 2017, A new disjunct Dendrothrix (Euphorbiaceae, tribe Hippomaneae): a Guiana Shield element in sub-Andean cordilleras of Ecuador and Peru, PhytoKeys 86, pp. 117-130 : 119-125

Dendrothrix condorensis K.Wurdack sp. nov. Figure 2

Diagnosis.

Differs from Dendrothrix yutajensis in larger, thinner leaves with more secondary veins, percurrent tertiary venation, acuminate leaf apex, and seeds lacking a caruncle.

Type.

ECUADOR. Zamora-Chinchipe: Nangaritza. Cordillera del Cóndor region, upper Rio Nangaritza valley , along road 14.5 km south of Guayzimi , above west bank of Rio Nangaritza , sandstone slope with relatively low forest, canopy 20 m, forest being cleared for mining of silica sand for glass manufacture, 04°02'27"S, 78°38'44"W, 930 m, 25 Nov 2005 (fl, fr), D. Neill & W. Quizhpe 14939 (holotype QCNE; isotypes: AAU, GB, HUT, K, LOJA, MO-6106711, NY, US).

Description.

Shrub or small tree to 8 m tall, monoecious; stems of leafy branchlets 2-3 mm dia., bark smooth, pith soft. Exudate present, white latex. Indumentum of multicellular trichomes to 0.1 mm long, ramified, dark reddish-brown. Leaves alternate, petiolate, stipulate, simple. Stipules free, paired, scale-like, 0.5 × 0.3 mm (width at base), triangular, persistent, eglandular. Petioles 40-65 × 1-2.5 mm (dia. mid-length), terete, adaxially slightly canaliculate towards distal end, petiolar glands absent. Leaf blades: laminar size class mesophyll, blade 14.5-19.8 × 6.5-8 cm, length:width ratio 2.00-2.98 (mean = 2.63, n = 11), symmetrical, shape elliptic, apex angle acute, apex shape short acuminate to attenuate, base angle acute, base shape cuneate to obtuse; margin entire, slightly revolute; blades sparsely pubescent when mature (young leaf not seen), primary and secondary veins more densely so; lamina thin and brittle when dry, adaxial surface smooth except for prominulous venation, abaxial surface pale, dull due to minute papillae; basilaminar glands present, abaxial, one on each side of primary the vein at the attachment of petiole and hidden under minutely auricled extension of lamina, narrowly elliptic, 1.4-1.8 × 0.4 mm, shallowly sunken into laminar surface and without raised edge, gland surface smooth; embedded laminar gland-like structures (perhaps necrotic, see Discussion), 0-6 per leaf, abaxial, scattered but usually adjacent to secondary or tertiary veins in distal portion of lamina, circular to widely elliptic, 0.5 × 0.3-0.4 mm. Venation pinnate, brochidodromous, 18-22 secondaries per side, spacing mostly regular, secondary vein angle gradually increasing along the series from ca 0° for proximal secondaries to 30° for distally diverging veins, course usually straight until curving for distal <1/4 of length, insertion shortly decurrent; intersecondaries parallel to secondaries, infrequent (1-5 per side); intercostal tertiaries alternate percurrent (occasionally opposite); primary to tertiary veins slightly prominulous on both surfaces. Inflorescence terminal, erect, compound thyrse, 21-31 cm long, with 2-3 orders of branching, axes moderately pubescent; leaves at base of inflorescence often of reduced size; lateral branches usually bisexual (rarely staminate) with pistillate flowers proximal and staminate distal, branch nodes subtended by usually eglandular bract (rarely at more distal nodes with pair of glands similar to those on cymules); bract acuminate, 2-2.5 × 0.5-0.7 mm (width at base). Staminate cymules spirally arranged, 20-22 per lateral inflorescence branch, subtended by bract and pair (1 on each side of bract base) of elongate disc- or cup-shaped glands; bract to 1 (deep) × 2 mm (wide), elliptic, margin sparsely ciliate; glands of proximal cymules 1.2-2 × 0.8-1.5 mm, becoming smaller at distal cymules (unclear if the size decrease is due to serial reduction or decreasing maturity), fleshy, 0.1 mm thick when dried, surface smooth and without pores; bracteoles absent. Staminate flower buds 10-16 per cymule, tightly clustered, erect when emergent from subtending bract, globose, to 0.7 mm diameter just before opening; anthetic flowers articulate at base, shortly pedicellate on persistent pedicel to 0.5 mm long; sepals 2 (rarely irregularly 3), connate at base to 0.3 mm, distal lobes 0.4-0.6 × ca 0.5 mm, margin sparsely ciliate; stamens 2(-3), 1-1.5 mm long, barely protruding beyond calyx at anthesis; filaments connate, 0.8-1 × 0.1 mm; anthers 0.4-0.5 mm long, bithecate, apicifixed to subapicifixed with very short connective and pendulous thecae, longitudinally dehiscent via slit 1/2-2/3 length of thecae; pistillode absent; flowers yellow in life. Pistillate flowers solitary at 1-2 proximal nodes of lateral thyrse branches; subtending bract 2-2.5 × ca 1.5 mm (width at base), acuminate; bract glands present (distal flower) or reduced to absent (proximal flower), similar to those subtending staminate cymules; short pedicellate, pedicel 0.5-0.8 × 0.5-0.6 mm; flower 3.5-4 mm long; sepals 3, 2-2.5 × 1 mm, free to minutely connate at base (to 0.2 mm), cymbiform, narrowly acute tip, sparsely pubescent, margin sparsely ciliate; ovary 3-locular, ovoid, 1 × 1 mm, top tapering, densely pubescent, distinguished from styles by change in pubescence density; styles connate into trigonous column 1.5-2 × 0.5-0.7 mm, sparsely pubescent; stigmas 3, undivided, slightly flattened, 0.7-1.1 (long) × 0.3 (thick) × 0.4 mm (wide at base), recurved to coiled at anthesis, surface coarsely papillose; placentation apical pendulous with a single ovule per locule; staminodes absent. Infructescence consisting of primary axis with lateral fruiting nodes, distal staminate portions of lateral branches deciduous; fruit pedicels 1-2(3) × 0.5-0.7 mm; bracts persistent. Fruit subglobose, 5 × 7 mm, sparsely pubescent, apex trilobed due to sunken stylar region, ventral (septal) sutures sulcate, dorsal (loculicidal) sutures with slight ridge; mericarps equal, 2-valved, splitting septicidally then loculicidally to release seeds; sepals, styles, and stigmas persistent. Pericarp dry, woody, mericarp wall 0.3 mm thick (equatorial at dorsal suture); exocarp extremely thin (ca 0.05 mm) but locally thickened to 0.2 mm along ventral suture, adherent to mesocarp on dehiscence; mesocarp woody, in equatorial section varying from 0.3 mm thick at dorsal suture to 0.7 mm toward ventral suture; septa woody, nearly continuous except for distal semicircular gap where traversed by funicle, 0.7-1 (wide) × 0.3-0.4 mm (deep); mericarp valves (cocci) remaining attached together after dehiscence via basal triangle 1 × 1-1.3 mm (width at base), slightly twisted when dehisced; septa of mericarps with one bifurcate vascular strand; funicle short, stout, 0.3 × 0.3 mm; columella (carpophore) persistent, 5 × 0.45-0.5 mm (width at narrowest point in middle), dilating to 1-1.5 mm at both tip and base, trigonous, narrowly alate. Seeds 3 per fruit, dry, ellipsoid, 4 (long) × 2.7 (wide; lateral-lateral) × 2 mm (deep; raphe-antiraphe); apex with short beak, flattened or depressed around hilar zone, ventral face with shallow groove along which raphe runs as ca. 0.1 mm wide prominulous line; testa dry, smooth, uniformly dark brown, thin (ca 0.05 mm thick); caruncle absent; embryo not seen.

Etymology.

The specific epithet refers to the Cordillera del Cóndor, where the type was collected. The mountain range name in turn comes from “condor” based on “kuntur” (Quechua) and refers to the Andean condor ( Vultur gryphus L.), an important part of the ecology and culture of the Andes.

Distribution and ecology.

The new species mostly occurs at 800-1000 m in dense, low, wet forest and sclerophyllous scrub over nutrient poor, acidic, sandstone-derived soils. Such habitats resemble those in the Guiana Highlands occupied by D. yutajensis . The three well-separated localities (Cordillera del Cóndor, Cordillera Escalera, Cerro Teyu; Fig. 1 ) are discoveries due to recent exploration in remote sub-Andean cordilleras, and continued floristic work is likely to extend its range to similar habitats further south in Peru. Floristic affinities between the Cordillera del Cóndor and Cordillera Escalera are notable ( Neill et al. 2014). Flowers and fruits were collected during September-November and flowers in March (also fruits in July fide Croat 91402, not seen). Dendrothrix yutajensis with more collections to finely document phenology, is reproductive from November to May and appears to flower and fruit continuously during this period.

Conservation status.

Following the criteria and categories of IUCN (2012), D. condorensis is given a preliminary status of Vulnerable (VU) under geographic range criteria B2 area of occupancy <2000 km2 (B2a, known to exist at no more than 10 locations; B2b, continuing decline projected). Threats to this taxon in the Cordillera del Cóndor include mining for the underlying silica sand. The Cordillera Escalera is protected as a conservation area.

Additional collections.

ECUADOR. Zamora-Chinchipe: Nangaritza, Cordillera del Cóndor region, west side of upper Río Nangaritza, along road about 13 km south of Guayzimi, silica mine "La Daniela", dense wet forest on sloping Hollín sandstone plateau, being mined for silica sand for glass manufacture, 04°08'35"S, 78°35'45"W, 970 m, 15 Sep 2007 (fl.), D. Neill, C. Davidson, S. Christoph & W. Quizhpe 15747 (AAU, LOJA, MO, NY, QCNE). [Same locality], 15 Sep 2007 (fr.), D. Neill, C. Davidson, S. Christoph & W. Quizhpe 15750 (AAU, GB, LOJA, MO, NY, QCNE, US). Along road from near Paquisha south to Las Orchídeas, and end of river at Río Nangaritza, via Guayzimi, beginning at 15.9 km E of Zumbi and Río Zamora, then 37.3 km S of junction, 12.3 km N of Las Orchídeas, 04°08'25"S, 78°38'31"W (-4.1402700, -78.6419400), 886 m, 17 July 2004 (fr), T. Croat, L. Hannon, G. Walhert & T. Katan 91402 (MO; not seen but tentatively included here based on TROPICOS record). PERU. Amazonas: Bagua District, upper slopes and summit of Cerro Teyu, summit with sclerophyll scrub, 05°15'56"S, 78°22'07"W, 1030 m, 22 Mar 2001 (fl.), H. van der Werff, R. Vasquez & B. Gray 16331 (MO, US). Loreto: Alto Cahuapanas, Campsite #3 ("Alto Cahuapanas") on Rapid Biological and Social Inventory #26, -5.66438889, -76.839, 1000-1350 m, 28 Sep 2013, M. Ríos Paredes 3480 (F). [Same locality], 29 Sep 2013, M. Ríos Paredes 3517 (F).

Discussion.

The four species of Dendrothrix are morphologically similar, and major differences are presented in Table 1 . Dendrothrix condorensis and D. yutajensis are likely closely related as they have nearly identical floral features. However, they are easily distinguished by foliar characters (i.e., size, shape, thickness, and details of leaf architecture), seed caruncle differences, and biogeography. Although leaf architecture has not been rigorously compared through clearings and anatomy, several orders of the varyingly prominulous venation are evident in unprepared specimens that allow gross comparisons such as were shown by Esser (1993) to be informative for the group. In D. condorensis , secondaries are 18-22 pairs, mostly straight with few course deflections, and distally curving upward for <1/4 of course; intersecondaries are rare, and tertiaries are percurrent (Fig. 3G ). In D. yutajensis , secondaries that are fewer (usually 7-9 pairs), not straight due to a slight zigzag (fractiflexuous) appearance where tertiaries diverge, and distally curving upward for half of their course; intersecondaries and frequent, and tertiaries are reticulate (Fig. 3J ). Even on unusually robust specimens of D. yutajensis (e.g., Maguire & Maguire 35103, US), the largest leaves (16.5-18 × 6.5-7.8 cm) have only up to 11 pairs of secondaries. The leaves of D. condorensis more closely resemble those of D. multiglandulosa Esser with which it shares the generally larger blades and percurrent venation. Dendrothrix multiglandulosa is only known from two collections from the Cuao-Sipapo massif in Venezuela and potential variation is poorly understood. Dendrothrix yutajensis is the most frequently collected and wide-ranging species of Dendrothrix , known from many well-separated tepuis, but intraspecific variation appears low. Dendrothrix wurdackii Esser has previously unrecognized intraspecific variation with an odd collection (i.e., BRAZIL, Pará: km 872 Cuiabá-Santarém [Highway], Serra do Cachimbo, forest beside small stream, 6 Nov 1977, G. Prance 24947, MO, NY, US), having much larger (to 18 × 8.5 cm), long acuminate, glabrous leaves with poorly developed abaxial micropapillae as compared with the four other collections of the species that closely resemble the type. This collection, which Grady Webster annotated as a new species of Senefeldera Mart., clearly has closest affinities with D. wurdackii based on similarities in leaf shape and venation, basilaminar glands, pistillate sepal shape, and biogeography. While the morphological differentiation and slight disjunction (Fig. 1 ) may be significant, it is not to the degree used here to justify the recognition of D. condorensis and I have refrained from further taxonomic adjustments until D. wurdackii is better understood.

Leaf micromorphological features are similar among the taxa of Dendrothrix . The distinctive, loosely attached, branched trichomes (Fig. 3E, K ) are structurally very similar but can differ in pigmentation (rusty brown versus whitish; see Table 1 ). Epidermal microrelief such as micropapillae or striations that give an often light-colored, matte sheen to abaxial leaf surfaces has evolved in many genera of Euphorbiaceae , including Dendrothrix , and other hippomanoids (e.g., Gymnanthes hypoleuca Benth., Sebastiania larensis Croizat & Tamayo, Senefelderopsis croizatii Steyerm.). The microrelief likely has functional significance related to optimized stomatal conductance and reduced leaf wetting ( Neinhuis and Barthlott 1997). The morphology of the leaf micropapillae in Dendrothrix is unusual and may be synapomorphic. They have positional size variation in being short to absent on major veins and grading to longer in intercostal regions (Fig. 3K ). In D. condorensis , the micropapillae are finger-like, 25-30 μm tall, ornamented with ridges, and form a protective canopy that obscures the stomata (Fig. 3H-I ). Epicuticular waxes are not well developed, in keeping with the non-glaucous appearance. The stomata are only abaxial, with the adaxial surface being relatively featureless (Fig. 3I ). Glands are often present on leaves and/or inflorescences of Euphorbiaceae , and Dendrothrix is no exception where they occur in pairs at the base of the leaf and subtending the bracts. The nature of scattered laminar glands in Dendrothrix is partly unclear. In the case of D. wurdackii they resemble typical Euphorbiaceae laminar glands with a well defined raised border and an abaxial distribution adjacent to secondary veins towards the leaf margin. The glands on Prance 24947 contain drops of clear exudate that are still sticky after 40 years. I have not found clearly homologous structures on the other taxa of Dendrothrix . Circular to widely elliptic, small (<0.5 mm diameter), gland-like structures with smooth surfaces and without raised edges are sparsely present in D. condorensis and more abundantly so in D. multiglandulosa , where in the latter they were considered of systematic significance ( Esser 1993). Although not examined anatomically, these appear to be wound response to microbial damage rather than typical glands as evidenced by their absence in the few young leaves available, erratic distribution, the presence of apparently intermediate epidermal blistering stages that are clearly necrotic, and margins that are not clean under SEM (not shown) but rather contain fragments that suggest micropapillae residue from surficial degradation.

Among reproductive characters that are variable among the species are details of the pistillate flowers including sepal and stigma morphology (see Table 1 ). Staminate bract glands vary in number with Dendrothrix multiglandulosa usually having 2-3 pairs (variable from 1-4, and paired or unequal in number between the bract sides), while the other species have one pair ( D. yutajensis rarely has a second gland on one side, e.g., Maguire & Maguire 35103, NY). Inflorescence branching is potentially variable, with 2-3 orders for D. condorensis and D. multiglandulosa , and the other species have only two orders. It is unclear if this represents noteworthy interspecific variation or possible collector bias for smaller inflorescences that better fit herbarium sheets. Dendrothrix is characterized by staminate flowers with two connate anthers (Fig. 4D-E ). Rare flowers with three anthers are present on collections of D. condorensis (i.e., Neill & Quizhpe 14939, MO) and D. yutajensis (i.e., Maguire & Maguire 35103, NY). Such flowers have more or less symmetrical androecia, connate filament columns, partial third sepals, and developed pollen, which indicates they may be functional despite being teratological in gross structure (Fig. 4F ). The triandrous flowers may be of significance in reflecting the likely plesiomorphic condition for the tribe and the ease of merosity change even in groups that appear fixed. The bract glands are smooth and without pores (Fig. 4B-C ). The staminate sepals bear stomata and are externally minutely papillose (Fig. 4A ). The pollen of Dendrothrix (Fig. 4G ; Esser 1994) is tricolporate with a perforate exine, which closely resembles that of other Hippomaneae (see Park and Lee 2013). Seed variation occurs among the taxa of Dendrothrix (Fig. 3A-D ) with a wider, more globose seed in D. multiglandulosa , and a well-developed caruncle in D. wurdackii . In D. yutajensis the caruncle is small, and there is no caruncle in D. condorensis or D. multiglandulosa . The 13 available seeds of D. condorensis from dehisced fruits (some slightly immature; note lighter brown coat in Fig. 3B relative to other samples) do not show evidence of caruncle growth (Fig. 3F ), while all seeds that I examined of D. yutajensis have a small caruncle.

Dendrothrix has a noteworthy Guiana Shield disjunct distribution (Fig. 1 ), which now combines two patterns with its over 1000 km distant outliers including elements in both the Andean (i.e., D. condorensis ) and Amazon (i.e., D. wurdackii ) phytogeographic regions. Such a tripartite distribution does not appear to be shared with other Guiana Shield near-endemic plant genera, although many have disjunct species in just one of those regions ( Berry and Riina 2005). Raveniopsis Gleason ( Rutaceae ) also has a distribution of Guiana Shield endemics and two Brazilian Amazon lowland outliers, and interestingly, one of the few localities of D. wurdackii ( Calderón et al. 2682, NY) is also the type locality for one of those outliers, Raveniopsis campinicola Kallunki ( Calderón et al. 2722, US).

Figures

Figure 1. Distribution map of Dendrothrix in northern South America.

Figure 2. Illustration of Dendrothrix condorensis. A Habit B Leaf base (abaxial) showing basilaminar glands C Staminate cymule D Staminate flower E Pistillate flower F Cross section of ovary G Portion of infrutescence H Mericarp valve I Seed. (Source: A Neill et al. 15747, MO and using life photos of this collection; B, E-F van der Werff et al. 16331, MO; C-D, G Neill & Quizhpe 14939, MO; H-I Neill et al. 15750, MO).

Figure 3. Seeds and surfaces of Dendrothrix. A-D Ventral views of seeds (ca = caruncle) A D. yutajensis B D. condorensis C D. multiglandulosa D D. wurdackii E D. condorensis, inflorescence axis showing dendritic trichomes F D. condorensis, top of seed showing short funicle (f) and caruncle absence G Abaxial view of D. condorensis leaf H D. condorensis transverse fractured leaf showing abaxial papillae and stomata (st), above intercellular space in the spongy parenchyma (m = mesophyll) I D. condorensis abaxial leaf micropapillae contrasting with smooth revolute adaxial leaf margin at image top J Adaxial view of D. yutajensis leaf K D. wurdackii, abaxial leaf surface along secondary vein showing gradient of micropapillae development at vein edges, and overlying dendritic trichomes. (A-D, F-G, J imaged with a Olympus DSX 100 E, H-I, K imaged with a Zeiss EVO MA 15 SEM at 10 - 12 kV after sputter coating with 25 nm of Au / Pd; SEM samples untreated and directly mounted from dried herbarium specimens. Source: A Nee 31120, NY; B, F Neill et al. 15750, MO; C Maguire & Politi 27683, NY; D Calderon et al. 2682, US; E, G-I Neill & Quizhpe 14939, MO; J Amaral 1523, MO; K Cid Ferreira 5797, NY).

Figure 4. Floral morphology of Dendrothrix condorensis. A Staminate sepal outer surface showing papillae and stomata (st) B Staminate cymule base showing subtending discoid gland C Surface of staminate cymule gland D Staminate flower E Staminate flower F Triandrous flower, top view of slightly asymmetrically fused androecium G Pollen. (Source: SEM of Neill & Quizhpe 14939, MO).