Radula mittenii Steph. Hedwigia 23: 148. (1884)

Renner, Matt A. M., Devos, Nicolas, Patino, Jairo, Brown, Elizabeth A., Orme, Andrew, Elgey, Michael, Wilson, Trevor C., Gray, Lindsey J. & Konrat, Matt J. von, 2013, Integrative taxonomy resolves the cryptic and pseudo-cryptic Radula buccinifera complex (Porellales, Jungermanniopsida), including two reinstated and five new species, PhytoKeys 27, pp. 1-113 : 45-49

Radula mittenii Steph. Hedwigia 23: 148. (1884) Figs 19 -21

Type.

Australia: Zaintree River [orthographical corruption of Daintree River], Pentzke s.n. 1882, herb. Mitten (lectotype [designated here]: Element 2, separated as subpacket within NY00831342!)

Description.

[From NSW897201] Forming extensive pure sheets of interwoven pendulous shoots on tree trunks and rocks; living plants opaque yellow-green to glaucous brown-green, fading to milky pale-brown in herbarium; shoot systems regularly pinnate, subdimorphic, with shoots 1.6-2.5 mm wide and up to 80 mm long, branches typically slightly smaller in stature than parent shoot; older shoot sectors becoming ragged in appearance due to irregular leaf fragmentation. Stems 190-250 µm diameter, with cortical cells in a single tier of 30-50 rows; cell walls brown pigmented throughout; cortical cell walls heavily and continuously thickened, at times constricting the cell lumen, dorsally arranged in an oblique zig-zag on young shoot sectors, cell elongation somewhat obscuring this pattern in mature shoot sectors; medulla cells in 80-110 rows, cell walls heavily thickened with coarse nodular trigones that become confluent, and constrict the cell lumen, thin walls occasional. Leaf insertion exceeding dorsal stem mid-line, insertion lines interlocking over two dorsal cortical cell rows, dorsal leaf-free strip absent. Leaf lobes oblong-falcate, 770-1360 µm long by 560-870 µm wide, contiguous to weakly imbricate, acroscopic base sharply deflexed away from stem, otherwise leaves weakly convex, not interlocking over the dorsal stem surface, stem visible in dorsal view, margins may be irregular in outline but always entire, the interior lobe margin curved, not auriculate, antical margin shallowly curved, exterior margin broadly rounded, postical margin straight or substraight. Lobules on leading shoots typically one quarter the lobe area, more or less quadrate, 430-720 µm long by 510-750 µm wide, keel straight to shallowly arched, angle between keel and stem 135°, keel turning through 45-55° at the apex; interior free margin weakly ampliate, acroscopic margin straight or shallowly arched, usually more or less perpendicular to shoot axis, and apices obtuse or broadly acute; attached to stem along 0.4-0.5 of the interior margin, stem insertion gently S-shaped but abruptly revolute at acroscopic end; lobule apex bearing a single papilla, with another papilla situated on the interior lobule margin above the stem insertion; lobules on leading shoots typically larger than those on branches, lobules on branches more rhomboid than quadrate, one fifth to one quarter the lobe area, keel shallowly arched to straight to slightly curved, angle between keel and stem 135°, keel turning through 45-55° at the apex, interior free margin weakly ampliate, acroscopic margin typically S-shaped to shallowly arched, inclined to shoot axis, apex typically broadly acute. Leaf lobe cells rotund to rounded-oblong, 19-28 µm long by 15-23 µm wide, thin walled with concave to triangular trigones, medial wall thickenings absent; cells of lobe margin smaller than those of leaf middle, quadrate to rectangular, 10- 15 µm long by 7-11 µm wide, long axis orientated parallel to lobe margin, exterior cell walls each with a medial wall thickening that bulges into the cell lumen margin; cell surface weakly bulging, bearing heavy verrucose ornamentation. Oil-bodies not known. Asexual reproduction by caducous leaf lobes, sporadic, typically but not always on old shoot sectors, fragmentation scars irregular, shoot primordia forming as irregular buds on leaf lobe margins in older shoot sectors prior to leaf fragmentation. Dioicous. Androecia on lateral branches that continue vegetative growth, androecial bracts in 3-5 pairs, smaller than vegetative leaves, lobes 510-660 µm long and 360-430 µm wide, ovate, imbricate, lobules hypostatic, keel deeply curved, bearing 1-2 antheridia each. Gynoecia terminal on axes, with one pair of female bracts subtended by one (on branches) or two (on leading shoots) full sized subfloral innovations that may again be fertile; archegonia 160-200 µm tall, archegonia neck five cell tiers, cells regularly arranged, 18-20 per gynoecium on a small raised disc of tissue encompassed by the base of the protoperianth; female bracts equal, ovate-falcate, lobes 1200-1310 µm long by 685-870 µm wide, lobules ovate, one half the lobe area, apex rounded to obtuse, keel strongly arched, insertion interlocking both dorsally and ventrally, insertion equitant. Perianths 3000-3500 µm long and 800-900 µm wide at mouth, cyathiform, flaring widely from a narrow base, which is a low stem perigynium 4-5 stratose with brown-pigmented walls, broadest immediately above base, straight-sided, gradually tapering to the mouth, which has irregularly sinuous labia; perianth walls 2-3 stratose at base, unistratose above; calyptral perigynium present, unfertilised archegonia ‘riding’ onto base of calyptra, calyptra 2-3 stratose at base, tapering to unistratose above.

Etymology.

Named for William Mitten (1819-1906) pharmaceutical chemist and bryologist, contemporary of and collaborator with W.J. and J.D. Hooker, father-in-law to Alfred Russell Wallace; and author of the first floristic treatment of liverworts of New Zealand in Hooker’s Handbook of the New Zealand flora.

Distribution and ecology.

In Australia Radula mittenii is known from a range of localities in the Wet Tropics Bioregion of north-eastern Queensland. Radula mittenii occurs over a broad elevational range, from near sea level to 1500 m, encompassing an array of tropical forest types from lowland mesophyll forests on river floodplains, to cyclone disturbed forests on hillslopes, to notophyll-vine forests on summit peaks. Within these habitats Radula mittenii occupies a range of microsites, from boulders, to tree trunks, and branches, twigs, and liane stems. As a lithophyte on the sides of large boulders Radula mittenii may form extensive pendulous mats of milky yellow-green shoots.

Variation.

Within individuals the dimorphic nature of shoot systems means lobules on primary shoots differ in size and shape from those on secondary shoots, a feature first documented by Renner et al. (in press) that is widespread among species of subg. Radula , Volutoradula and Cladoradula . Lobules on secondary shoots tend toward transverse rectangular shape, and the development of a reflexed antical lobule margin, which causes the lobule apex to appear acute. Plants from exposed situations, including those growing on branches and twigs, may appear to consist only of tangled shoots lacking architectural regularity, bearing lobules of this type, and so differ considerably from the lush, regularly pinnate plants found on rocks and tree-trunks in forest interiors. Close inspection of plants from exposed situations will reveal a primary shoot closely appressed to the substrate from which secondary branches arise. Comparison with plants from sheltered situations will reveal commonalities in the shape and size of lobules from secondary shoots.

Recognition.

Among Australasian Radula , Radula mittenii is easily recognized by its large size, regularly pinnate branching, more or less quadrate lobules, verrucose ornamentation on leaf-lobe cell surface, and the leaf-insertion interlocking over the dorsal stem mid-line. highly distinctive, and easily recognized species. The outstanding feature of Radula mittenii is the verrucose ornamentation that it imparts a milky yellow appearance to plants in life and in herbaria. However, colour is not always a reliable guide to identity.

Radula mittenii shares with Radula sumatrana Steph. A number of characters, including shoot size and branching architecture, the verrucose cuticle, and the large more or less quadrate lobules, and the two are probably closely related. However, the type of Radula sumatrana (G00112217!) differs in that the lobules tend to become much larger, imbricate, and obscure the stem surface in ventral view. This is consistent with other specimens seen from Borneo.Yamada describes stem cell walls of the type of Radula sumatrana as being thin-walled with large trigones. Thin walls in the stems of Australian material examined are rare, and in general trigones are more confluent and less discrete than illustrated by Yamada (1974). Radula sumatrana occurs throughout South East Asia from Thailand to Indonesia including Sumatra, Java and Borneo ( Yamada 1979), and plants corresponding to it do not occur in Australia. However, in the unlikely circumstance that these two names do refer to the same entity, Radula mittenii has priority.

Some forms of Radula mittenii bear resemblance to the type specimen of Radula similis (G00042714!) in their lobule shape and smaller stature. However, Radula similis , a taxon from New Caledonia,has apparently smooth leaf lobe cell surfaces, so is readily distinguished on this basis. However, granular ornamentation in some species of subg. Radula can be very difficult to detect with some light microscopes, and we may have missed this feature. At any rate if ornamentation is present, it is not as pronounced as in Radula mittenii .

Radula mittenii canbe differentiated from members of the Radula buccinifera complex on the basis of many characters, including 1) the verrucose lobe cell surfaces, in Radula buccinifera the lobe cell surfaces are smooth or bear low dome-shaped papillae; 2) the presence of heavy, continuous, irregular, brown-pigmented secondary thickenings on the medullar cell walls of the stem formed by fusion of nodular trigones, in Radula buccinifera the medullar walls are pigmented or not, and if secondarily thickened bear trigones that rarely fuse to form irregular continuous thickenings, 3) the large quadrate lobules on leading shoots one quarter the lobe area, in Radula buccinifera complex the lobules are one eighth to one fifth the lobe area and are rhomboid, not quadrate; 4) the production of caducous leaves, all members of the Radula buccinifera complexbar Radula anisotoma lack specialised means for asexual reproduction; 5) the regular pinnate, subdimorphic branching of female plants, in the Radula buccinifera complex female plants are irregularly or pseudodichotomously branched, as a function of patterns of subfloral innovation production (male plants may be pinnately branched).

Radula mittenii could be confused with a number of related species that occur in the wet tropics of north Queensland, however as the identity of several of these has not yet been fully resolved, the differentiation of Radula mittenii from these species will be dealt with in a subsequent treatment of Radula reflexa .

Nomenclature.

In the protologue of Radula mittenii Stephani states Radula mittenii is 'Dioicous, robust 4-5 cm long, olivaceous, rigid, regularly pinnately branched, branches remote, short. Leaf-lobes obliquely patent, contiguous, subrotund, concave, apices inflexed, dorsally longitudinally adnate, subauriculate … [lobule insertion] long decurrent, lobule base inflated, exterior margin truncate’, and in notes states that "Die Form der lobuli ist fast genau die der Rad. recubans, welche aber viel längere Bätter hat." [the form of the lobule is similar to Radula recubans , which however has longer leaves].

Stephani (1884) identified a single specimen gathered by Pentzke in 1882 from the 'Zamtree River’ held in the herbarium of Mitten as the type of Radula mittenii , in so doing effectively identified a holotype. Zamtree River is a lexigraphical error for the hand-written locality on the holotype, which is “Zaintree”. This is a corruption of ‘Daintree’, the river immediately south of Cape Tribulation in north Queensland.

In this holotype (NY00831342) are three elements: two separate pieces of material and three shoots loose within the packet. These three elements comprise three different Radula species.

The first element has shoot systems that are sparingly dichotomously branched, and lobules whose interior margin is not ampliate over the stem, and in these characters it does not agree with the protologue.

The second and third elements are pinnately branched, and lobules with inflated base and truncate exterior margins, so agree in some pertinent details with the protologue. However, besides the description of shoot length, the protologue is insufficiently detailed to discriminate between elements two and three. Element two has shoots approaching 50 mm long which element 3 does not.

Of the three elements only two, the first and second, are known to occur in the vicinity of the Daintree River. The third is a southern temperate species whose northern limit is somewhere in the vicinity of the Clarence River, northern New South Wales.

As there is not much basis, beyond shoot length, for selecting between elements 2 and 3 given the protologue, Article 9, Recommendation 9A.4 of the ICN could be invoked, to preserve current usage of the name Radula mittenii , as a synonym of Radula buccinifera following Yamada (1984), as the third element is this species. However, Radula buccinifera does not occur at the Daintree River, from where the holotype was collected, and the holotype contains other elements that do occur there, one of which agrees with the protologue, making this undesirable. Lectotypification of the name Radula mittenii on the second element capitalizes on an available name for a species that has not otherwise been described. Historical misinterpretation of Radula mittenii , particularly by Castle (1967), is immaterial as Yamada’s proposed synonymy with Radula buccinifera resolved this at the specimen level. This means the name Radula mittenii has no current usage to preserve. We therefore lectotypify Radula mittenii on that element agreeing with the diagnosis and originating from the type locality, being element two within NY00831342, which is separated as a subpacket.

Of the other elements, the first corresponds to Radula notabilis M.A.M.Renner, described below and the third, comprising three loose shoots within the packet corresponds to Radula buccinifera .

The origin of these three loose Radula buccinifera shoots is unclear - based on current knowledge of Radula buccinifera 's distribution it cannot have come from the Daintree River region. The most likely explanation is that the type in Mitten’s herbarium comprises an aggregate of material from two geographical locations. It is not known how this mixing may have occurred, however there is in MEL a collection, also attributed to Pentzke in 1882 from the Daintree River, and this is a large mat of pure Radula buccinifera . We can rule no explanation for the attribution of Radula buccinifera to the tropics out at this stage. Mitten’s specimen was communicated from the Phytologic Museum of Melbourne by F. von Mueller, and it is possible the contamination, and confusion, occurred at the time duplicates were made. A duplicate of Pentzke’s collection ex herb. Mitten in herb. Stephani (G00067469!) also contains a shoot of Radula buccinifera , including branches, as does another duplicate ex herb Steph in BM (BM000969294!), these specimens can therefore be regarded as duplicates of the type specimen but are not isolectotypes because they do not contain the element upon which the name is lectotypified.

Specimens examined.

Australia, Queensland: Cook District, Leo Creek, upper Nesbit River, 13°33'S, 143°28'E, 420 m, 20 Aug 1948, L.J. Brass 19954, MEL1037795, as Radula acutiloba ; Cook District, McIlwraith Range, N of Lankelly Creek at point c. 20 km from Coen, 13°53'S, 143°15'E, 5 Aug 1978, G. Butler 591, CANB7806509; Cook District, Daintree River National Park, Mossman Gorge, Rex Creek, 16°28'S, 145°19'E, 15 Jul 1994, E.A. Brown 94/482 et al., NSW297090; Cook, Daintree National Park, Mossman Gorge, Rex Creek, upstream from swingbridge, 16°28'13"S, 145°19'42"E, 105 m, 24 Mar 2012, M.A.M. Renner 6282, V.C. Linis & E.A. Brown, NSW896665; Cook District, on trees, near Fallons, Cairns, Oct 1890, C.J. Wild, BRI-AQ722874 as Radula javanica ; Cook District, Smithfield, 2 Jul 1890, (?) C.J. Wild, ex herb. C.J. Wild, BRI-AQ722872 as Radula javanica ; Cook, Wooroonooran National Park, Bellenden Ker Range, North Babinda Creek, Goldfields track, on tree trunk 10 cm dbh, 65 m, 17°20'8"S, 145°51'59"E, 3 Apr 2012, M.A.M. Renner 6486, V.C. Linis, E.A. Brown, NSW897201; 6 km W of Babinda, The Boulders, 17°21'S, 145°53'E, 80 m, 3 Dec 1990, J.A. Curnow 3737, NSW389069 as Radula buccinifera , BRI; Mt. Bartle Frere, 14 Jul 2005, M.A.M. Renner 2020 & E.A. Brown, NSW867312; ibid, M.A.M. Renner 2021 & E.A. Brown, NSW897314; North Kennedy, Tully Gorge State Forest, tributary of the Tully River, 17°46'S, 145°35'E, 220 m, 1 Aug 1995, E.A. Brown 95/129 et al., NSW390388; North Kennedy, Tully Gorge, 17°46'S, 145°34'E, 2 Jul 2005, E.A.Brown & M.A.M. Renner 1822, NSW869299; Byfield, N of Emu Park, 7 Apr 1949, O. Selling S-B178020; ibid, 1 Jun 1949, O. Selling, S-B89670 as Radula buccinifera det M.-L. So; Cook, Wooroonooran National Park, Bellenden Ker Range, North Babinda Creek, Goldfields track, 17°20'08"S, 145°51'59"E, 65 m, 03 Apr 2012, M.A.M. Renner 6489, V.C. Linis & E.A. Brown, NSW897206; Cook, Daintree National Park, Mossman Gorge, Rex Creek, 16°28'11"S, 145°19'37"E, 105 m, 24 Mar 2012, M.A.M. Renner 6288, V.C. Linis & E.A. Brown, NSW896672; Cook, Daintree National Park, Mossman Gorge, Rex Creek, 16°28'11"S, 145°19'37"E, 105 m, 24 Mar 2012, M.A.M. Renner 6296, V.C. Linis & E.A. Brown, NSW896685; Cook, Wooroonooran National Park, Babinda Stream, Goldfields track, 17°19'54"S, 145°51'52"E, 75 m, 03 Apr 2012, M.A.M. Renner 6497, V.C. Linis & E.A. Brown, NSW909664; 18 km SSW of Cardwell, Broadwater Forest Park, 18°25'S, 145°56'E, 60 m, 30 Nov 1990, J.A. Curnow 3608, NSW389070 as Radula buccinifera (dups BRI-AQ807558, CANB9408694); ibid, J.A. Curnow 3610, NSW389071 as Radula buccinifera ; 18 km SSW of Cardwell, Broadwater Forest Park, 18°25'S, 145°56'E, 65 m, 30 Nov 1990, H. Streimann 45379, CANB90133854; Kennedy South, Eungella National Park, Finch Hatton Gorge, 21°04'S, 148°38'E, 225 m, 22 Jun 2005, M.A.M. Renner 1534 & E.A. Brown NSW866081.

Figures

Figure 19. Radula mittenii line drawings. A Lobe marginal cells B Lobe medial cells C Ventral view of female shoot D Transverse section of stem from primary shoot E Dorsal view of primary shoot F Three lobules from primary shoots G Four lobules from secondary shoots H Shoot primordia and regenerating shoot from leaf-lobe margin I Ventral view of androecium J Cellular detail of lobule apex K Female bracts L Archegonium M Ventral view of perianth-bearing shoot. N. Perianth mouth O Transverse section of perianth. Scale bars: A-B: 40 µm, D, J, H, L: 60 µm. C, E, I, M: 600 µm, F, G, K, N: 240 µm, A-H, J from NSW 867314. I, K-O from BRI-AQ 331973.

Figure 21. Radula mittenii pictures 2. A Ventral view of male shoot B Androecium on tertiary shoot C-H Ventral view of lobules on secondary shoots. All from NSW 897201.