Drymoanthus adversus

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Drymoanthus adversus
Conservation status
Not Threatened (NZ TCS)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Monocots
Order:	Asparagales
Family:	Orchidaceae
Subfamily:	Epidendroideae
Genus:	Drymoanthus
Species:	D. adversus
Binomial name
Drymoanthus adversus (Hook.f.) Dockrill
Synonyms
Newzealochilus adversus (Hook.f.) R.Rice Sarcochilus adversus Hook.f. Thrixspermum adversum (Hook.f.) Rchb.f.

Drymoanthus adversus (commonly known as 'fleshy tree orchid') is a small orchid species endemic to New Zealand.^[2]. It has a wide distribution throughout the country, where it grows as an epiphyte or lithophyte in a range of habitats.

Drymoanthus adversus plants are approximately 4–15 centimeters in diameter ^[3] with thick, fleshy leaves with occasional purple spots. The leaves are elliptical or round with pointed tips and a deep central vein. Its leaf arrangement is alternate, with the overall leaves appearing in a "V" shape. The base of the leaves is connected to the leaf sheath along a clearly defined abscission line, and the old leaves are slightly drooping.

The stem of D. adversus is very short, usually only 5 cm long. Its fleshy aerial roots are green to grayish white, and the can grow very long. The root system is radiating and closely attached to the bark. The inflorescence of D. adversus grow opposite to the tip of the plant, often drooping down into a raceme, which is 80 millimeters long, with 16–20 flowers. The flowers are green to greenish white, sometimes with red or purple spots. Sepals and petals are nearly equal in length, about 3.5x1.5 millimeters.^[4] Lips are almost equal in length and wider, very fleshy, upright, with a smooth convex outer surface and deep grooves. The middle lobe is free and only serves as a small cup-shaped tip.^[5] Successful pollination results in a solid elliptical fruit with parallel grooves.

Drymoanthus adversus is found throughout New Zealand, ranging from the southernmost Stewart Island to the northernmost Motukokako Island/Piercy Island. It is also found in the coastal areas and mountainous highlands of the Chatham Islands. In the North Island, it is abundant in the southernmost and northernmost peninsulas, and is absent from small areas centered around National Park, Waipukurau, and Blairlogie. On the South Island, it is mainly distributed along the west coast, mountains and forests from north to south; its east coast distribution is more limited, but a small number of individuals have been observed in Maungati and Dunedin.^[6]

Drymoanthus adversus often grows in moist forests near rivers or oceans, and chooses tree trunks and branches on ridges shrouded in thin mist or clouds as habitats.^[7] Drymoanthus adversus grows on a range of host plants including the vine Metrosideros fulgens, shrub Lophomyrtus obcordata, and tree fern Dicksonia squarrosa. It is also found growing on trees in cultivation. According to Cox & Lehnebach's observations, the number of D. adversus increases with the increase of host surface area.^[8] Drymoanthus adversus does not tend to favor specific host species, but rather tends to favor the size of the host, most commonly found on larger trees. D. adversus often grows together with moss lichens on tree trunks, and almost 90% of them come into direct contact with these non-vascular epiphytic plants. Moss also serves as a substrate for orchids to provide moisture, but the lowest proportion of orchids growing in contact with each other is on the shrub Olearia paniculata. Orchid roots typically grow into lichens and mosses. ^[8]

Like many epiphytic orchids, Drymoanthus adversus requires an environment with high humidity and sufficient sunlight. As epiphytic orchids, the outer epidermis of the host is an important environmental factor. The texture of the bark, the age of the host, and chemical substances in the bark may affect seed germination, distribution, and abundance.^[9] Drymoanthus adversus is found on a wide range of trees including native and introduced species. Its roots are often observed intertwined with moss and lichen. Crain^[10] hypothesized that moss, as a living substrate for orchids, can provide water for epiphytic orchids and support fungal growth. Fungi are crucial for the germination of orchid seeds, and the habitat preference of orchid mycorrhizal fungi adds another level of complexity to the interaction between orchids and hosts.^[11] The orchid mycorrhiza association is mutually beneficial; orchids provide fungi with sugars and B vitamins, while fungi provide water, minerals, and more than 80% of the plant's carbon needs. Perhaps it is because lichen is a symbiotic body of algae and fungi, similar to mosses, that lichen also helps establish orchid seeds.^[12]

Drymoanthus adversus is classified as not threatened by the New Zealand Threat Classification System.

With the increase of vascular bundle epiphyte species on the host, the incidence rate of Drymoanthus adversus decreases and remains at a low level.^[8] D. adversus is potentially threatened by habitat loss as the result of plant disease; for example, Austropuccinia psidii (G. Winter) Beenken is a disease that spreads rapidly, causing deformation of leaves and branches, and the death of branches in infected trees.^[13] In this case, D. adversus could risk losing its host tree to infection.

Drymanthus adversus may have ornamental value as a horticultural plant, by tying it to wood with water moss and hanging it in a warm, shaded location. It is watered often until new roots grow and stabilize itself.^[14] Orchid collectors pose a threat to rare local orchids, and the large-scale collection of orchids can lead to a decrease in species diversity in the original regions.^[7]

adversus: From the Latin adversus ‘turned towards’, ‘before’ or ‘opposite’. The growth direction of inflorescence of Drymoanthus adversus is opposite to the whole plant.

Drymoanthus adversus flowers from September to January, and after successful pollination, it will bloom from November to May. The fruit forms from late December to January and matures slowly. Around July, the fruit completely ripens and begins to release seeds. At this time, new racemes will gradually develop and mature in preparation for the next pollination. The release of D. adversus seeds is assisted by the siphoning effect of the fluff inside the fruit shell.^[7] Orchid seeds are very small, and by discarding the cotyledons or endosperm that should have provided nutrients for germination in the seeds and compressing the embryo into small cell clusters without embryonic roots or buds, the cost of seed production is reduced, thereby increasing yield.^[15] This promotes long-distance seed dispersal by the wind. ^[16] Perhaps due to the fact that orchid seeds must associate with specific mycorrhizal fungi for germination and development, most seeds will be deposited near the parent plant, resulting in a higher survival rate. Seedlings can often be observed growing on the same trees as their parent plant, lower down the tree. ^[7]