Philodendron zhuanum Croat, sp. nov.
TYPE: Panama. Coclé: Alto Calvario, vic. El Copé, ca. 6 km N of El Copé, 770 m, 8E38'N, 80E35'W, 12 July 1994, Croat & Zhu 76755 (holotype, MO--4619357--9; isotypes, AAU, B, CAS, COL, CR, F, GH, K, MEXU, NY, PMA, QCNE, SCZ, US, VEN). Figures 465--468.
Planta hemiepiphytica; internodia 2--4 cm longa, 3--5.5 cm diam.; cataphylla 37--50 cm longa, acute 2-costata, decidua; petiolus 40--63 cm longus, obtuse D-formatus, in sicco manifeste complanatus usque 3--6 cm latus; lamina anguste ovato-sagittata, 38--62 cm long, 27--32 cm wide; inflorescentia 3; pedunculus 9--14 cm longus, 1--1.5 cm diam.; spatha 13--18.5 cm longa, lamina spathae alba, intus suffusa magentea in triente inferiore; tubo spathae extus viridi, intus atriviolaceipurpureo; pistilla 8--9-locularia; loculi 1--3-ovulati.
Hemiepiphytic, loosely or appressed-climbing; leaf scars conspicuous, 3 cm long, 2 cm wide; internodes semiglossy, 2--4 cm long, 3--5.5 cm diam., dark green, drying dark brown, longitudinally wrinkled; roots drying light brown and weakly glossy, finely striate, epidermis peeling; cataphylls 37--50 cm long, sharply 2-ribbed, medium green, semiglossy, drying dark brown, deciduous; petioles 40--63 cm long (0.8--1.5 times longer than blades), bluntly D-shaped, faintly raised medially, moderately firm, medium green, surface dark green short-lineate, drying dark yellowish brown and glossy, prominently flattening to 3--6 cm wide and only a few mm thick, smooth to finely and closely striate; sheath 3--6 cm long, moderately closed; blades narrowly ovate-sagittate, moderately coriaceous, acuminate at apex, conspicuously sagittate at base, 38--62 cm long, 27--32 cm wide, (1.8--2 times longer than wide), margins broadly undulate, much paler than surface, upper surface dark green, glossy, drying dark yellowish brown, lower surface weakly glossy, paler, drying reddish brown to yellowish green with conspicuous, dark intermittent secretory canals visible; anterior lobe 34--35 cm long, margins broadly convex, paler; posterior lobes 8.5--18.5 cm long, 7--13 cm wide, directed downward to slightly inward, broadly rounded; sinus narrow, spathulate to narrowly obovate, (7.5)15--19 cm deep, 1--3 cm wide; major veins drying with sharp ridges, usually darker than surface; midrib flat, paler than surface above, narrowly rounded, concolorous below; basal veins (3)5--6 per side, with the first free to base numbers 3--5 coalesced (2)5--7 cm; posterior rib not at all naked or naked to 2.5 cm; primary lateral veins 6--7 per side, arising at an acute angle then spreading to a 40--45E angle, weakly arcuate until near the margin, then turned up abruptly, weakly sunken above, convex, paler than surface below; minor veins clearly visible, arising from both the midrib and primary lateral veins, drying prominulous above, faint and weakly wrinkled below. INFLORESCENCES 3 per axil; peduncle 9--14 cm long, 1--1.5 cm diam., somewhat flattened, medium green, faintly short-lineate; spathe 13--18.5 cm long, margins paler; spathe blade white, except yellow-green medially on back side outside, tinged magenta on lower one-third inside; spathe tube medium green outside, dark violet-purple inside, spadix 11.5--18 cm long; pistillate portion creamy green, 3.5--8 cm long, 3--6 cm long in back, 1.5 mm diam. at apex, 1.9 mm diam. at middle, 1.8 mm wide at base; staminate portion 8--10 cm long; fertile staminate portion slightly narrower than the pistillate portion; sterile staminate portion barely distinguishable when fresh, 1.2--1.3 cm diam. at base, tapered only slightly upward when fresh (drying to 10 mm diam. at apex); pistils 1.9--2.1 mm long, 1.2--1.6 mm diam.; ovary 8--9-locular, 0.8 mm long, with basal placentation; locules 0.8--1.2 mm long; ovules 1--3 per locule, translucent, contained within gelatinous matrix (no true envelope), 0.3--0.4 mm long, equal in length to funicle, style similar to style type B; stylar canals emerging directly onto surface; style apex truncate; stigma short, covering entire style apex; the androecium truncate, margins irregularly 4--6 sided, 0.8--1.2 mm diam. at apex; sterile staminate flowers irregularly rounded, 0.8--1 mm wide.
Flowering in Philodendron zhuanum is documented by a single collection from July, at the beginning of the rainy season. A cultivated plant of the same collection flowered in November at the Missouri Botanical Garden.
Philodendron zhuanum is endemic to Panama in Coclé Province in an area of Premontane rain forest at 700 to 900 m elevation.
Philodendron zhuanum is a member of P. sect. Calostigma subsect. Macrobelium ser. Macrobelium. This species is distinguished by its short, thick internodes, deciduous, sharply two-ribbed cataphylls, bluntly D-shaped petioles about as long as the blades or slightly shorter, narrowly ovate blades with prominent posterior lobes, a narrow sinus and prominently visible secretory canals, up to three inflorescences per axil, and spathes green outside and whitish inside on the blade, and dark purple-violet inside on the tube.
Philodendron zhuanum is apparently related to both P. sagittifolium and P. aromaticum, differing from both in having petioles which on drying become moderately spongiose, markedly flattened (especially in the middle portions), dark yellow-brown to yellowish, and often glossy. It also differs in having conspicuous secretory canals visible in both living and dried conditons. While secretory canals are present in both P. sagittifolium and P. aromaticum, they are quite inconspicuous.
This species is perhaps most easily confused with P. aromaticum which has similar leaf blades with a naked posterior rib. The latter species occurs at lower elevations and nearer the coast. In contrast, P. zhuanum rarely has the posterior rib naked. While P. zhuanum has the spathe tube dark purple-violet inside with the same color bleeding onto the lower one-third of the blade, the spathe tube of P. aromaticum is white to weakly maroon within and the color does not merge onto the lower part of the blade.
Philodendron zhuanum is named in honor of Guanghua Zhu, my student, field companion and monographer of the genus Dracontium, who helped to collect the type and many other aroids during our field work in Panama.
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Additional specimen examined.
PANAMA. Coclé: Alto Calvario, vic. El Copé, ca. 5 mi. N of El Copé, 900--1000 m, Croat 75054 (CM, MO).