Monolena primulaeflora - Cactus Club

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Monolena primulaeflora

Plant of the Month > Species I to M

by Bruce Brethauer

   This month’s plant is a bit of a departure from the usual fare. While this species does produce a large succulent caudex, it grows under conditions far different from the desert and near desert habitats from which many of our succulent plants originate; indeed, this species grows in the rainforests of Ecuador and Peru and, and contrary to appearances, will not tolerate any significant drought.

   By any standard, this is a striking plant, producing large, satiny, lance shaped, puckered foliage. New foliage is emerald green, but soon darkens to a dark moss green. The underside of the foliage of mature leaves is contrastingly colored red or magenta. The foliage is borne on long, fleshy, wine to burgundy colored petioles.

   The flower buds are produced on long arching spikes which are also burgundy to wine colored. The developing flower buds are initially protected by large, transparent, greenish bracts; these eventually open to reveal buds with pale pink to light magenta petals. It is my recollection that the flowers only open briefly - perhaps for only a few hours: Flowers are smallish, measuring from about 1 to 1.5 inches across, with translucent pink to pale magenta petals with darker magenta veining. To my eyes, the flowers are similar to a "double" flower of an African violet, or a Tradescantia (Spiderwort), although its specific epithet would suggest that these flowers bear a similarity to those of primroses. Each spike may produce about 18 or so flowers in succession. Even though individual flowers are short lived, a large, established plant will produce a number of spikes, with many successive blooms so that the entire display may last several weeks. A well gown, mature plant will have several flowering periods each year, and some plants may produce a few flowering spikes between these other displays, so that these plants will have at least one or two stalks in flower through much of the year.

   The flowers are followed odd triangular fruits measuring to perhaps ½ inch across, each one producing approximately one hundred small (practically dust-like) seed. Seen from above, these fruits are arranged so that adjacent fruits are tightly nested producing an almost zipper-like pattern.

   Plants produce a large irregular caudex which may grow 2 to 3 inches tall, and spreading to many inches (the largest caudex which I have seen to date measures over 8 inches, but it is my understanding that the caudex will spread continually as the plant grows, and therefore it is conceivable that plants may produce caudexes which may spread two feet or more across). The caudex grows above ground, but under normal circumstances, it is usually at least partially concealed beneath dense foliage, so the caudex may not be readily visible in all plants.

   Another odd trait of this species, is that plants produce minute spherical "pearl bodies" on the underside of their leaves. These are rich in proteins, and are avidly eaten by a number of ant species. It is believed that plants of Monolena primulaeflora have a symbiotic relationship with ants: the plants provide these protein rich "pearl bodies" to attract ants to the plant, and it is believed that the ants may benefit the plant by removing a variety of insect pests. It is also possible that ants may assist in pollinating flowers, and in dispersing the seed of this species.

   This species requires warm temperatures, moist and humid conditions, and bright indirect light for best growth. Despite producing large, succulent caudexes, these plants are intolerant of drought, and should never be permitted to dry out. These are great plants for well lit terrariums - provided of course that you can provide a terrarium which is large enough. These will grow into large plants with leaves rising more than 14 inches above the soil line, and with a widely spreading caudex. I have grown a plant in a covered aquarium, and later, grew a potted plant in a shallow pan of water, keeping the lowermost portions of the pot continually wet so that the plant never was subjected to drought. Exposed to drought - even a drought of short duration, and this species will loose foliage, and may even loose roots. Plants will often become dormant in response to even minor drought, so keeping the plants moist and humid is one of the most important factors in growing this species well. Plants also benefit from uniformly warm temperatures, and high humidity, and seem to grow best when provided bright, indirect light. While the most impressive plant which I have seen was grown in a tropical greenhouse with frequent misting, I have grown a plant under fluorescent lights in my basement. Lights need to be positioned just a few inches above the plants foliage: fluorescent lights will provide both light and warmth, although some additional warmth from a heating mat may be necessary for best growth, as this species thrives under warm conditions (with temperatures in the mid 80's by day and the mid to lower 70's by night). This species also benefits from high humidity, and should be grown on top of a pebble tray filled with water and gravel to increase the humidity, and should be given frequent misting - particularly in winter when most homes have particularly low humidity. Plants require an extremely coarse potting mix to promote rapid root growth, and good circulation of air to the roots. Many growers recommend the same fir and cork bark mediums which are used in growing orchids, although I have used a potting medium consisting of roughly equal parts of coir fiber, Pearlite, and Turface All Sport with good results. I have found it best to water plants frequently - never allowing the soil, or roots to become dry. As I have already indicated, subjected to even modest drought, this species will quickly respond by dropping leaves, and may become dormant as well. I have had good results in growing one plant with its pot set in a shallow tray filled with water, and I suspect that plants will grow quite well in hydroponic culture.

   Where this species is happy, growth can be quite rapid, so it is probably necessary to give plants frequent applications of fertilizer - particularly during the summer months, when growth is usually most rapid. While I have used the same fertilizer which I use on all of my succulents (Dyna Gro Bloom), a fertilizer with a somewhat higher percentage of nitrogen (perhaps to 10 or 15 percent) may prove to be better for this species. In summer, I have fertilized as often as every 2 weeks - making an application diluted to approximately 1/4 the recommended rate. But even in winter, I have fertilized regularly - usually about once every 4 weeks. Where plants can be provided with warm conditions year round it is not necessary to encourage plants to become dormant, but when plants are frequently exposed to cooler air, they will tend to drop a significant portion of their leaves and go dormant on their own. Even when dormant, the plant should never be subjected to conditions of drought. Plants will usually break dormancy when provided with brighter light and warmer temperatures, but this is not always the case - sometimes the plants may require a little coaxing to break dormancy such as more frequent watering, or more frequent applications of fertilizer.

   While I frequently recommend that growers move their plants outdoors in the summer to benefit from increased exposure to daylight, and higher temperatures, it has been my experience that this plant does not appreciate direct sunlight, which will often cause its leaves to scorch. Instead, this species should be moved into a sheltered site with open shade or dapple sunlight. Plants of this species seem to be sensitive to cool temperatures, and should be brought indoors again in late summer or early fall - before temperatures regularly fall below 60 degrees Fahrenheit.

   At present, plants are rather hard to come by in the trade, although I have seen plants in several unexpected places (including one of the plants grown in a display of frogs at the Columbus Zoo). The Glasshouse Works in Stewart, Ohio regularly offers plants, and occasionally offers a second clone with distinctly marked veining on its foliage. Several years ago, I donated my plant to The Ohio State University, so I no longer grow a mature plant of this species, but since that time, I have collected seed produced from that plant, and have germinated these, so sometime in the near future, I hope to be able to share seedlings with other members and guests at one of our Society meetings.

   Monolena primulaeflora is an attractive plant with bold foliage, colorful petioles, abundant flowers in pink and magenta produced in several waves through the year, plants also produce large succulent caudexes. It has a great appeal to several different categories of specialist growers - those who like foliage plants, tropical flowers, those who specialize in caudex producing plants, and those few of us who are interested in the various types of ant plants. It is nevertheless a plant which is not suited to all growers - its needs for continually moist, warm and humid conditions and bright but indirect light makes it a challenge to grow in many households, but I find it to be such an unusual and attractive species, that I would recommend it to anyone who is interested in trying something a bit more unusual than the standard fare.

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