Lygodium

Page, Christopher N., Collinson, Margaret E. & Van Konijnenburg-Van Cittert, Johanna H. A., 2014, Lygodium hians E. Fournier (Pteridophyta, Schizaeales) - an endemic unusual groundclothing member of a modern climbing fern genus in New Caledonia, Adansonia (3) 36 (1), pp. 21-43 : 32-34

COMPARISON WITH LYGODIUM RETICULATUM AND LYGODIUM MICROPHYLLUM

On the basis of morphological comparison of herbarium materials held at RBG Kew, UK, the most similar other species in the genus Lygodium to L. hians seems to be L. reticulatum . L. reticulatum bears its sorophores mainly laterally and to a degree around the tips of its fertile lamina, thus appearing somewhat intermediate between L. hians and most other Lygodium . L. reticulatum is, however, a much more typical Lygodium , with the sporophyte life-cycle concentrated upon much more extensive development of climbing fronds into which vegetative and fertile functions of the plant are mainly focussed, and ecologically specialised to forest-margin habitats at mostly mid- to low altitudinal range. The reticulate venation pattern of the sterile fronds differs from the non-reticulate, dichotomous venation in L. hians fronds ( Fig. 4A ; 5B ). L. reticulatum spores are reticulate, with a slightly more pronounced sculptural pattern on the distal than on the proximal surface (van Konijnenburg-van Cittert 1991, 1992). Their reticulum is quite regular, and thus different from the very irregular, verrucate-reticulate sculpture of L. hians . They measure between 80 and 120 µm in diameter and are thus slightly smaller than L. hians spores. L. reticulatum also occurs in New Caledonia, and is additionally present more widely, ranging to the New Hebrides, northern Queensland and the Polynesian islands (e.g., Copeland 1929, 1932, Brownlie 1969, and herbarium data).

Another species L. hians should be compared with, is L. microphyllum , also in the subgenus Odontopteris . Although dissimilar to L. hians in general morphology with its typical climbing fronds, it is one of the very few Lygodium species that bears its

sorophores all around the margin, from the base of the fertile lamina to the tips (e.g., Copeland 1929, 1932, and herbarium data). Its spores are smaller than those of L. hians and L. reticulatum , c. 85 µm in diameter, with a slightly more rugulate than reticulate morphology (van Konijnenburg-van Cittert 1981).

SYNTHESIS OF LYGODIUM HIANS CHARACTERISTICS Hence the combination of examination of this colony of L. hians , plus that of known herbarium material from all other known localities, clearly demonstrates:

– the existence of an exceptional life-form in Lygodium ;

– the ability of this determinate-fronded life-form to achieve extensive ‘ground-clothing’ local development;

– the nature of this ability to persist (semi-permanently) as a member of a rainforest floor vegetation community;

– the unusual position of sorophores grouped terminally and sub-terminally on fertile fronds;

– that spores are irregularly verrucate to rugulate to irregularly reticulate characteristic of those of Lygodium subgenus Odontopteris ;

– that the most closely comparable modern species is L. reticulatum , which differs in having reticulate frond venation, regularly reticulate spores and a more typical climbing frond growth form.

Figures

FIG. 4. — Herbarium sheets from other collections of Lygodium hians E.Fournier including lectotype: A, herbarium sheet of Lygodium hians from Mt. Arembo (New Caledonia) showing both a dichotomous determinate ground-clothing frond and a climbing fertile frond, the latter with terminal and sub-terminal sorophores (MNHN,P00630569, Herb. P); B, lectotype of Lygodium hians from Mt. Humboldt (New Caledonia),showing a climbing frond with terminal and subterminal sorophores (MNHN,P00523232, Herb.P).Sheet height:42 cm.

FIG. 5. — Blade details in Lygodium hians E.Fournier from Plateau de Dogny, New Caledonia: A, long blades from Figure 2A showing morphology and basal dichotomies; B, blade from Figure 2A showing various arrangements of lateral vein departure from mid-vein, open dichotomous venation with up to two dichotomies, and denticulate margin with vein endings not related to position of marginal teeth; C, tip of short blade from right frond in Figure 2A showing insect damage and wound reaction tissue. Page 23222, Herb E. Scale bars: A, 1cm; B, 2 mm; C, 1 mm.