Sciaphila

Abstract: The floral units of Triuridaceae, commonly regarded as flowers, may equally plausibly be interpreted as pseudanthia, i.e., modified and highly reduced partial inflorescences. This hypothesis is new for Triuridaceae, but earlier authors have noted strong similarities between the inflorescences of Cyclanthaceae and Pandanaceae (Pandanales) and the putatively pseudanthial floral units of some Alismatales (e.g., Potamogeton). The morphology of the floral units of Triuridaceae, particularly the female and hermaphrodite structures, closely resembles a smaller version of a Pandanus pistillate inflorescence. In some species of Pandanus, the female flower consists of a single uniovulate carpel with a single stigma, as in Triuridaceae. This striking morphological similarity is remarkable in the context of recent evidence from a single 18S nuclear rDNA sequence for Sciaphila that placed it as sister to Pandanaceae within Pandanales. However, because pseudanthia have been reported in both Alismatales and Pandanales, ...

Abstract: The star-like root system of the achlorophyllous Sciaphila polygyna (Triuridaceae) consists of roots up to 1.4 mm thick and 1 cm long seemingly radiating from a single origin. Internally, the roots show a bilateral symmetry when viewed in cross-section: the third root cell layer contains rather loose coils of the aseptate mycorrhizal fungus from the dorsal to the lateral sides, in contrast to the extremely dense coils of thin hyphae in its ventral part. Additionally, the hyphae develop vesicle-like swellings mainly in the central part of the dorsal side as well as the lateral parts of the third layer. The fourth root layer is anatomically heteromorphic, having exceptionally large cells, reaching up to 320×130 μm in size (giant cells), in the lower lateral parts. The root-colonizing hyphae only degenerate in the fourth layer, most readily in the giant cells, where they may swell to 24 μm in diameter, collapse and end as amorphous clumps. Hyphae in the third layer keep their definite structure. The structures are interpreted to be the result of a dynamic reaction of the root to the actual fungal penetration points in order to maximize the benefit from the subsequent colonization by compartmentation of the root tissue. The function of the third layer is to host the fungus and keep it alive within its cells, while mainly the giant cells serve for its digestion. Many indications suggest an arbuscular mycorrhiza for this association. Similarities and differences to other myco-heterotrophic species are discussed.

Abstract: With a reduced need for photosynthesis, the plastome of parasitic and mycoheterotrophic plants degrades. In the tiny, fully mycoheterotrophic plant Sciaphila thaidanica, we find one of the smallest plastomes yet encountered. Its size is just 12,780 bp and it contains only 20 potentially functional housekeeping genes. Thus S. thaidanica fits the proposed model of gene loss in achlorophyllous plants. The most astonishing feature of the plastome is its extremely compact nature, with more than half of the genes having overlapping reading frames. Additionally, intergenic sequences have been reduced to a bare minimum, and the retained genes have been reduced in length both compared with the orthologous genes in another mycoheterotrophic species of Sciaphila and in the autotrophic relative Carludovica.

Abstract: Borneo is known to have the greatest diversity of the mycoheterotrophic genus Sciaphila (Triuridaceae), harboring nine species, with three endemics. Here, we report two previously undescribed species of Sciaphila discovered during botanical surveys in Lambir Hills (Sarawak, Borneo, Malaysia) and provide detailed morphological accounts of these new species: S. alba and S. inouei. We also provide a key to the species of Sciaphila in Sarawak.