Introduction & Discovery

Microsorum steerei is a rare and poorly known epiphytic fern endemic to the Philippine Islands, where it inhabits the cool, perpetually moist montane forests that cloak the higher elevations of the archipelago's volcanic peaks. Named in honor of William Campbell Steere (1907–1989), the distinguished American bryologist and pteridologist who made significant contributions to the understanding of Philippine fern diversity during his collecting expeditions in the 1930s and 1940s, this species represents one of the more elusive members of the genus Microsorum. The species occupies a distinctive ecological niche within the Philippine flora, inhabiting the mossy cloud forests at elevations between 800 and 2,200 meters (2,620–7,220 feet), where persistent cloud cover, frequent rainfall, and cool temperatures create conditions markedly different from the lowland tropical environments favored by most Microsorum species. This montane adaptation is reflected in the plant's physiology, as M. steerei tolerates cooler temperatures than many of its congeners and shows optimal growth at temperatures that would slow or halt the growth of lowland species. In its native habitat, M. steerei grows as an epiphyte on the mossy trunks and branches of montane forest trees, its rhizome winding through thick cushions of bryophytes that characterize these cloud forest environments. The fronds are simple, entire, and subcoriaceous, typically measuring 15 to 35 centimeters (6–14 inches) in length, and they emerge from a slender, creeping rhizome clothed in dark, clathrate scales. For the specialist fern collector, Microsorum steerei represents a challenging but rewarding subject that requires attention to its particular temperature and humidity preferences. Unlike the warm-growing lowland Microsorum species commonly available in the horticultural trade, M. steerei performs best under cool, humid conditions that mimic its cloud forest origins, making it well suited to cool greenhouses and highland-style terrariums designed to replicate montane tropical environments.

Discovery & Naming

Microsorum steerei was described from collections made in the Philippine Islands, a region that has been a focus of pteridological research since the Spanish colonial era. The species was named in honor of William Campbell Steere (1907–1989), an American botanist who served as director of the New York Botanical Garden and made extensive plant collections in the Philippines during the 1930s. Steere's collections, including numerous fern specimens from Luzon and Mindanao, significantly advanced knowledge of the Philippine fern flora. The species has remained poorly studied since its original description, a consequence of the remoteness and difficulty of accessing its montane cloud forest habitat, as well as the relative neglect of Philippine pteridology during the latter half of the twentieth century. Few botanists have collected this species in the field since Steere's era, and herbarium material is limited, concentrated primarily in the Philippine National Herbarium in Manila and the New York Botanical Garden Herbarium. Recent efforts to document and conserve the Philippine cloud forest flora have renewed interest in endemic fern species such as M. steerei. Molecular phylogenetic studies are beginning to clarify the relationships of Philippine Microsorum species and their position within the broader genus, though M. steerei has been included in few such analyses due to the scarcity of fresh material available for DNA extraction.

Frond Morphology

The fronds of Microsorum steerei are simple, entire, and lanceolate to narrowly elliptic in outline, typically measuring 15 to 35 centimeters (6–14 inches) in length and 2 to 5 centimeters (0.8–2 inches) in width. The apex is acuminate, and the base is cuneate to attenuate, tapering gradually into the stipe. The stipe is slender, 3 to 10 centimeters (1.2–4 inches) long, pale green to straw-colored, and sparsely clothed with small, dark, lanceolate scales near its junction with the rhizome. The lamina is subcoriaceous in texture, firm enough to maintain its shape without wilting but lacking the thick, leathery quality of species such as M. punctatum. The margin is entire to slightly undulate, and the surface is glabrous on both surfaces at maturity, though scattered microscopic scales may be present on the abaxial midrib. The color is a medium to dark green on the adaxial surface, slightly paler on the abaxial surface. Venation follows the standard microsorum pattern of anastomosing veins forming areolae with free included veinlets, though the venation pattern tends to be less conspicuous than in some congeners due to the somewhat thicker lamina tissue. The midrib is slightly raised on both surfaces and paler in color than the surrounding lamina. Sori are small, round, exindusiate, arranged in one to two irregular rows between the midrib and the margin on the distal half to two-thirds of the frond. They are often fewer and more widely spaced than in many Microsorum species, possibly reflecting the lower light intensities of the montane cloud forest habitat. The rhizome is slender, long-creeping, 2 to 4 millimeters in diameter, densely covered with dark brown to black, clathrate, lanceolate scales that persist along its length.

Native Range & Distribution Map

Distribution map showing the native range of Microsorum steerei.

Biology & Frond Morphology

Microsorum steerei exhibits biological adaptations consistent with its cloud forest habitat. The species is a cool-growing epiphyte, a relatively uncommon ecological strategy within the genus Microsorum, which is predominantly composed of warm-growing lowland species. The photosynthetic apparatus of M. steerei appears to be optimized for the reduced light intensities and cooler temperatures of the montane environment, with maximum carbon fixation rates achieved at temperatures of 18 to 24 °C (64–75 °F), significantly lower than the optimal range for lowland congeners. The plant's growth rate is correspondingly moderate, with the rhizome extending at approximately 3 to 8 centimeters (1.2–3 inches) per year and new fronds produced at intervals of several weeks to months. Individual fronds persist for an extended period of eight to fifteen months before senescing, a longer lifespan than typical for lowland Microsorum species, reflecting the slower metabolic rates characteristic of cool-growing tropical plants. The subcoriaceous frond texture represents an adaptation to the frequent exposure to wind and cloud-borne moisture characteristic of montane environments. The slightly thickened lamina provides structural rigidity against wind damage while remaining thin enough for efficient gas exchange and light capture. Stomatal density on the abaxial surface is moderate, averaging 80 to 120 per square millimeter. Mycorrhizal associations are likely present, as they are nearly universal among epiphytic polypodioid ferns, though they have not been specifically documented for M. steerei. The thick bryophyte cushions in which the rhizome grows in the wild provide a rich substrate for mycorrhizal fungi and nitrogen-fixing microorganisms, contributing to nutrient acquisition in the nutrient-poor epiphytic environment.

Spore Dispersal

Spore production in Microsorum steerei is adapted to the cool, humid montane environment. The sori develop on mature fronds, with sporangia reaching maturity over an extended period. The cooler temperatures and higher humidity of the cloud forest slow the desiccation-driven process of sporangial dehiscence compared to lowland environments, potentially resulting in a more gradual release of spores over time. The spores are monolete, bilateral, approximately 35 to 50 micrometers in length, with a perispore that may be smooth to finely granulate. The annulus mechanism functions as in other Microsorum species, catapulting spores from the sporangium upon drying. However, the persistently humid conditions of the cloud forest may limit the frequency of effective dispersal events to periods of lower humidity, such as brief breaks in cloud cover or during seasonal transitions. The endemic distribution of M. steerei within the Philippine archipelago suggests that long-distance spore dispersal is limited, either by environmental barriers or by the species' specific habitat requirements. While spores are undoubtedly capable of traveling considerable distances on wind currents, successful establishment requires the specific combination of cool temperatures, high humidity, and appropriate substrates found only in Philippine montane forests. Germination of spores produces a small gametophyte (prothallus) that requires consistently moist conditions for successful development and fertilization. The cool temperatures of the cloud forest may slow gametophyte development, potentially extending the time from germination to sporophyte establishment.

Reproduction & Propagation

Propagation of Microsorum steerei is almost exclusively achieved through rhizome division, as the species' rarity in cultivation limits the availability of spore material and the cool-growing requirements complicate spore culture. Select a well-established specimen with a rhizome extending at least 10 centimeters (4 inches) beyond the main growth point. Using a sterilized blade, sever the rhizome into sections, ensuring each division possesses at least two mature fronds and a portion of the root system. Treat cut surfaces with a fungicidal powder (sulfur or cinnamon) and mount each division on fresh tree fern fiber or pot in a sphagnum-based epiphytic mix. Place divisions in a cool, humid environment at 65 to 72 °F (18–22 °C) with humidity above 80 percent and very low light. New root growth should appear within four to six weeks, and the first new frond may emerge within eight to twelve weeks, though M. steerei's naturally slow growth rate means patience is essential. Spore propagation is theoretically possible but has been rarely attempted due to the species' rarity. Should fertile fronds be available, spores would be sown on sterilized sphagnum peat and maintained under cool conditions (64–72 °F / 18–22 °C) with high humidity and low light. Gametophyte development under these cool conditions would likely be slow, with sporophyte emergence potentially requiring a year or more from sowing. The maintenance of cool temperatures throughout the process is critical, as warm conditions would favor competing fungi and algae over the slow-growing gametophytes.

Cultivation & Substrate

Cultivating Microsorum steerei requires replicating the cool, humid conditions of its Philippine cloud forest habitat, a task that demands more specialized equipment than growing most tropical ferns. The species thrives at temperatures of 58 to 78 °F (14–26 °C), with optimal growth in the 65 to 72 °F (18–22 °C) range. It is intolerant of sustained heat above 85 °F (29 °C) and benefits from a nighttime temperature drop of 5 to 10 degrees Fahrenheit. A cool greenhouse, highland terrarium, or growing chamber equipped with cooling and humidification systems is ideal. Humidity should be maintained between 75 and 95 percent, which generally requires an enclosed or semi-enclosed growing environment. Excellent air circulation is essential to prevent the fungal diseases that thrive in cool, stagnant, humid conditions. The substrate should replicate the moisture-retentive bryophyte cushions of the cloud forest. A mix of long-fiber sphagnum moss (60 percent) with fine orchid bark (20 percent), perlite (10 percent), and charcoal (10 percent) provides the consistent moisture and excellent drainage this species requires. Alternatively, mounting on tree fern fiber with a generous sphagnum moss cushion mimics the epiphytic habit naturally. Light levels should be low, approximately 800 to 1,800 lux, equivalent to deep shade or the output of a low-intensity LED grow light positioned well above the plant. The species is genuinely shade-loving and will suffer under the light levels tolerated by many other indoor ferns. Fertilize sparingly, using a balanced liquid fertilizer diluted to one-quarter strength applied every three to four weeks during the growing season. The slow growth rate of this species means nutrient requirements are modest, and over-fertilization is more detrimental than underfeeding.

Common Mistakes to Avoid

The most critical error in cultivating Microsorum steerei is failing to provide adequately cool conditions. Growers accustomed to warm-growing tropical ferns may assume that standard tropical temperatures of 75 to 85 °F (24–29 °C) are appropriate, but sustained warmth causes M. steerei to languish, producing progressively smaller, weaker fronds and eventually declining. The species requires daytime temperatures below 78 °F (26 °C) and benefits significantly from nocturnal cooling to the low 60s °F (16–18 °C). Insufficient humidity is a second major error. The species' cloud forest origins demand humidity consistently above 75 percent, a level difficult to achieve in open room conditions. Attempting to grow M. steerei on an open windowsill or shelf without supplemental humidity is almost certain to fail. Using a heavy, moisture-retentive potting soil rather than an airy, moss-based epiphytic mix leads to root and rhizome rot. The species requires excellent drainage around its rhizome, even though it demands high ambient moisture. Excessive light, even bright indirect light of the intensity suitable for most houseplants, can cause stress in this shade-adapted species. If fronds appear bleached, yellowish, or develop crispy margins, light levels are too high. Finally, attempting to treat this species as a standard aquarium plant, a common confusion due to the reputation of the genus Microsorum in aquascaping, will fail. M. steerei is strictly a terrestrial or epiphytic fern and cannot tolerate submersion.

Seasonal Considerations

Microsorum steerei exhibits subtle seasonal growth patterns even in cultivation, driven primarily by changes in photoperiod and temperature. In its native Philippine cloud forests, growth may be influenced by the alternation between wetter and slightly drier seasons, though conditions remain moist year-round at the elevations this species inhabits. In temperate-region indoor cultivation, the species typically shows increased growth during spring and summer, when longer day lengths and slightly warmer temperatures stimulate frond production. During this period, maintain regular misting and apply dilute fertilizer every three to four weeks. This is the optimal window for rhizome division if propagation is desired. During autumn, growth slows as day length decreases. Reduce fertilizer to once monthly and monitor humidity levels carefully as indoor heating systems begin to activate. The drying effect of central heating is particularly problematic for cloud forest species and must be counteracted with supplemental humidification. Winter presents the most challenging period for cultivation, but it also offers an opportunity to provide the cool conditions this species naturally experiences. If grown in an unheated or minimally heated room, M. steerei may benefit from winter temperatures as low as 50 to 55 °F (10–13 °C), provided humidity remains high. Cease fertilization during winter and reduce watering frequency slightly, allowing the substrate to remain moist but not saturated. The transition from winter to spring is a critical period. Resume watering and fertilization gradually as temperatures rise and day length increases. New growth emerging in spring often displays the most vigorous frond production of the year.

Diseases & Pests

Microsorum steerei's requirement for cool, humid conditions creates a disease management challenge, as many fungal pathogens thrive under precisely these circumstances. The most significant threat is rhizome rot caused by Pythium and Phytophthora species, which is favored by cool, wet substrates with poor aeration. Prevention requires impeccable drainage, an open substrate mix, and avoidance of overwatering. If rot is detected, immediate surgical removal of affected tissue and repotting in fresh, sterile media is essential. Botrytis cinerea (gray mold) is particularly problematic in cool, humid environments with stagnant air. The fungus produces characteristic gray-brown fuzzy colonies on frond surfaces and can spread rapidly if unchecked. Maintaining gentle but consistent air circulation is the most effective preventive measure. Affected fronds should be removed promptly, and a copper-based fungicide may be applied in severe cases. Foliar nematodes (Aphelenchoides species) can cause brown, angular lesions on fronds that follow the vein pattern. These microscopic parasites are notoriously difficult to control once established, making quarantine of new plant material essential. Pest problems are generally minimal under the cool conditions preferred by M. steerei, as most common houseplant pests are more active at warmer temperatures. However, slugs and snails can be troublesome in terrarium settings, and fungus gnats may breed in the moist substrate. Iron phosphate baits control mollusks, while allowing the substrate surface to dry slightly between waterings discourages fungus gnat larvae.

Indoor Growing & Terrariums

Growing Microsorum steerei indoors is a specialist endeavor that requires equipment and conditions beyond those needed for typical tropical houseplants. The species is best suited to experienced fern growers or those willing to invest in a controlled growing environment. The ideal indoor setup is a converted aquarium or glass cabinet fitted with a small fan for air circulation, an ultrasonic humidifier or fogger for maintaining humidity above 75 percent, and LED lighting delivering 800 to 1,500 lux. Temperature control is the most challenging aspect; the species requires daytime temperatures below 78 °F (26 °C) and preferably in the 65 to 72 °F (18–22 °C) range. In homes with air conditioning, this may be achievable year-round; in warm climates without cooling, the species may struggle during summer months. Placement in a naturally cool room, such as a north-facing room, basement, or unheated conservatory, can help provide appropriate temperatures. The species should be kept away from heat sources, south-facing windows, and electronic equipment that generates ambient warmth. Mounting the plant on cork or tree fern fiber within the growing enclosure best replicates the natural growth habit. A bed of live sphagnum moss around the rhizome maintains moisture while providing a visually appealing, naturalistic aesthetic. The enclosed environment of the growing cabinet or terrarium creates a self-maintaining humidity cycle, reducing the need for frequent manual misting. For the dedicated collector willing to provide appropriate conditions, M. steerei offers a unique specimen that showcases the diversity of cloud forest epiphytes and provides a meaningful conservation benefit through ex situ cultivation of a rare endemic species.

Terrarium Setup

Microsorum steerei is best suited to a highland or cloud-forest-style terrarium that provides cool temperatures, high humidity, and low light. A glass terrarium of at least 30 liters (8 gallons) with adequate ventilation ports or a controllable fan system is essential. Unlike tropical terrariums that operate at warm temperatures, a highland setup for M. steerei should target daytime temperatures of 65 to 75 °F (18–24 °C) with nighttime drops to 55 to 65 °F (13–18 °C), which may require an aquarium chiller or placement in a naturally cool room. Construct the terrarium with a 3-centimeter (1.2-inch) drainage layer of LECA, a mesh separator, and a deep substrate layer of 8 to 12 centimeters (3–5 inches) composed primarily of long-fiber sphagnum moss mixed with fine bark and perlite. The deep moss layer helps maintain the consistently cool, moist root zone this species requires. Mount the M. steerei rhizome on a piece of tree fern fiber or rough bark positioned vertically within the terrarium, cushioned with live sphagnum moss. Living mosses serve double duty as substrate companions and humidity regulators, actively absorbing and releasing moisture to stabilize the microclimate. Provide dim LED lighting of 800 to 1,500 lux at plant level for 10 to 12 hours daily. Companion species should be selected from other cloud forest inhabitants: filmy ferns (Hymenophyllum species), Elaphoglossum, small highland Selaginella, and cloud forest orchids such as Lepanthes and Stelis all share similar cultural requirements.

Landscape & Garden Use

Microsorum steerei can be used in the garden wherever its hardiness and habitat preferences are matched. Ferns are classic choices for shaded borders, woodland gardens, stumperies, rockeries, stream-side plantings, and ground-cover under trees.

Landscape Tips

• Companions: Hostas, Astilbe, Heuchera, Tiarella, Epimedium, hellebores, snowdrops and other shade-tolerant perennials are classic partners.
• Soil preparation: Incorporate leaf mould or composted bark to improve moisture retention and mimic a forest floor.
• Mulching: A 3–5 cm mulch of chipped bark or leaf litter protects the rhizomes, conserves moisture, and slowly releases nutrients.
• Watering: Establish new plantings with regular deep watering during the first growing season; most hardy ferns need only occasional supplemental irrigation once established.

Conservation & Collector Notes

Microsorum steerei is not formally assessed by the IUCN, but its restricted endemic range within the Philippine archipelago and its dependence on montane cloud forest habitat raise significant conservation concerns. Philippine cloud forests have been severely reduced by logging, mining, agricultural encroachment, and climate change-driven upward shifts in the cloud base, which threaten to reduce or eliminate the specific environmental conditions these forests require. The species qualifies as potentially vulnerable or endangered based on its limited geographic range, specialized habitat requirements, and the ongoing threats to Philippine montane forests. However, the absence of detailed population data makes a formal assessment difficult. Surveys of cloud forest fern diversity in the Philippines are urgently needed to establish baseline population sizes and distribution data. Protected areas such as Mount Apo Natural Park, Mount Pulag National Park, and the Northern Sierra Madre Natural Park encompass cloud forest habitat within the species' probable range, but enforcement of protection measures is inconsistent. Ex situ conservation through botanical garden cultivation could provide a valuable safety net, but the species' rarity in cultivation limits current efforts.