Plants small to medium, shoots 350–800 µm wide. Branching irregularly pinnate; dimorphic branching, with both Frullania-type (FB) and occasionally, Lejeunea-type (LB) branching. Initial appendages of FB: First branch underleaf (BUL1) always with three distinct segments, the ventral lamina divided for 1/3–2/3 its length into two unequally or subequally sized lobes+ 1 dorsal saccate lobe; First branch leaf (BL1)usually± characteristic of normal stem leaves (i.e.BL1: 1 explanate dorsal lobe + 1 saccate lobule + 1 stylus), only rarely are the appendages of BL1 reduced in size and elobulate with leaves characteristic of the main stem starting at BL2–3. Initial appendages of LB: BUL1 and BL1–3 are always reduced in size and lobule-free; formation of normal lobulate leaves occurring thereafter. Stemleavesoften with incurved distal margins, and dorsal margins extending beyond the farther edge of the stem, rounded, subacute or apiculate apices and non-auriculate at the base, margins entire and surface smooth.Lobules ± remote from the stem, obliquely spreading at angles of ca. 30–60° with the stem so that lobules tilted outwards; lobules similar in colour to other organs; cylindrically pitcher-shaped; ca. 1/3 from lobule mouth there is a distinctly elongated cell in comparison to other marginal lobular cells, to 3.25X long as wide, ca. 20–30µm long; free margin of lobular mouth crenulate-sinuate. Stylus medium to large, to 20 cells in total, to 175 µm long × 125 µm wide, usually subtriangular. Lateral margins of underleaves usually entire, some phenotypes with small angulations or with 1 pair of small teeth on the lateral margins; apex of underleaf bilobed to 1/2 its length, lobes 4–10 cells wide at base, and rounded, acute to subacute apices.
Leaf lobe median cells with subequally thickened, hyaline walls, intermediate thickening rare to absent, cell cavities to ca. 10–18 µm long × 8–12 µm wide, to 1.2–2 × long as wide; cells becoming gradually larger basally. Median cells of underleaves ± subequally thickened so that the hyaline trigones and intermediate thickenings become indistinct. Median cells oflobuleslightly longer than wide, walls flexuose with indistinct trigones and small nodulose intermediate thickenings from the base of the lobule to the apex.
Plants dioicous. Androecia subspherical, discoid, or spicate, of 3–6 (9) pairs of bracts, sessile (stalk with no leaf lobes) or terminal on very short-stalked lateral branches (stalk with 1–5 vegetative leaf lobes). Gynoecia terminal on main or leading stem. A shoot system usually arising immediately below the set of 2–3 (4) progressively larger bracts and bracteoles below the gynoecium or perianth (subfloral branch), occasionally arising one or more vegetative leaf-cycles below the gynoecia or perianth bracts, i.e. a subfloral branch. Innermost bract unequally bilobed, bract-lobe entire, bract-lobule with 1 stylar tooth at the base, otherwise entire; innermost bracteole about 1/2 bilobed, entire. One or two archegonia per gynoecium. Perianth 3-keeled, surface smooth, and rim of beak also smooth, but the inner beak surface densely covered with large single-celled protuberances.
Cell surface of inner layer of the capsule wall with (1) 2-4 (6) large pores per cell forming deep indentations. Elaters to 40 in total. Spores globose, 37.5–50 µm at widest axis, which is interspersed with (7) 8–9 rosettes; each rosette 3–5 µm in diam., and bearing a ring of (6) 7–10 ± conspicuous primary stelae; the stelae to 0.75–2.25 µm high × 0.75–1.0 µm wide at base, tapering gradually to a rounded or subacute, hooked apex; stelae rarely divided in any form, and almost never bearing secondary deposits; the spore wall papillae otherwise densely distributed between rosettes.
Affinities, differentiation & variation: Frullania junghuhniana is part of a complex that includes Frullania junghuhniana var. bisexualis, F. junghuhniana var. minutissima, and its subvariety - subvar. monoica. This species appears to be very variable as is evident from the extensive synonymy of Frullania junghuhniana and its varieties. One common character that is shared by all the taxa of this complex is the distinct, elongated cell, to 3.25X long as wide, and up to 30 µm long and is situated immediately above the lobule mouth. However, the current taxonomic boundaries and classification of the species and its presumably close allies, i.e., its varieties, remains unsatisfactory and requires further investigation. This must involve detailed study of a greater number of specimens to determine the range of morphological variability, which is still uncertain.
Two infraspecific taxa have been historically recognised based solely on differences in sexuality. A reassessment of that philosophy must be undertaken and should include a combination of molecular and chromosome studies. Monoicous races of Frullania rostrata and other taxa have also been found, but in absence of any additional characters formal recognition of these has not been made until a better understanding of the biological principles involved, and how these should be treated taxonomically is critiqued.
Morphologically, Frullania junghuhniana and its varieties appear very similar to F. rostrata and the relationship is discussed under that species.
Geographic distribution: Hattori (1982b) summarised the distribution of Frullaniajunghuhniana var. junghuhniana to include: Java, Sumatra, Borneo, the Philippines, New Guinea, New Caledonia, and the Solomon Islands. Campbell (1997) also reported this species as a new record for New Zealand, but the specimens she cited are in fact F. rostrata. However, it remains possible that F. junghuhniana may indeed be present on the subtropical Kermadec Islands north of New Zealand.
Notes: Frullania mcveanii was described in detail by Hattori in 1973 and was only known from the type collection; Mt Wilhelm, New Guinea. Hattori noted that F. mcveanii was closely related to F. junghuhniana,but differentiated between them as follows. In well developed plants of F. junghuhniana: 1) the lobes of stem-leaves are rounded or widely obtuse and never acute at the apex, 2) intercalary (Lejeunea-type) branching absent, and 3) the cell walls of leaf-lobes are equally thickened; whereas in F. mcveanii: 1) the lobes of stem-leaves are acute, 2) Lejeunea-type branching often occurs, and 3) the cell-walls of the leaf-lobes are not very equally thickened. However, all the features Hattori used to distinguish F. mcveanii from F. junghuhniana in fact occur also in the latter species, therefore, F. mcveanii is reduced to synonymy under F. junghuhniana var. junghuhniana.