Male, Female and Hermaphrodite Carob Trees
Some carob trees do not bear any fruit, while others fill them with pods every year. The main reason for this is that carob is largely a dioecious species: male, female and hermaphrodite flowers are mostly found on separate trees. The male tree does not produce pods, but it provides pollen for female trees to bear fruit.
In this article, we discuss the types of flowers in carob, the characteristics of male, female and male trees, the ratios in natural populations, the recommended pollinator tree ratios in the garden and their effect on yield in the light of scientific sources.
Why is carob a "dioecious" tree?
In the vast majority of plants, both male and female organs are found in the same flower. In some species, male and female flowers are formed in separate individuals; this is called dioecularism in botany. Carob falls into this second group. According to the monograph published by IPGRI, carob is a dioecious species with some herbaceous forms; male, female and herbaceous flowers are usually found on different trees. Both unisexual and bisexual flowers are rarely found in the same cluster (Batlle and Tous, 1997).
This is not a common feature in the legume family. In the same source, it is stated that dioicity is not common among legumes and that unisexuality is generally seen as a trait derived from a bisexual ancestor from an evolutionary point of view. Dahmani et al. also state that carob flowers were initially bisexual, and in the later stages of development, they became functionally unisexual with the atrophy of the organs of a sex.
In practice, this means: Whether a carob tree bears fruit depends largely on its flower type. Male trees do not produce pods no matter how much they are cared for. Female trees, on the other hand, bear little or no fruit if there is not enough pollen supply nearby.
Carob Flower Types
Carob flowers are small, non-petal and reddish-green in color. Flower types are distinguished from each other by the following features (Batlle and Tous, 1997):
| Female flower | It consists of a pistil (female stamen) 6–8.5 mm long on a disc and vestigial stamens; around it are five hairy sepals. The curved ovary consists of two carpels and contains numerous seed outlines; the stigma is two-lobed. |
| Male flower | It bears five slender stamens around a nectar-secreting disc; a vestigial pistil is located in the middle of the disc. |
| Hermaphroditure flower | It bears both a developed pistils and five stamens; it is like a combination of two types. |
The flower structure may seem complex at first glance. Classifications based on observations in Cyprus refer to five types of panicles: two separate types of male panicles with long and short stemmed stamens, herbaceous panicle, female panicle, and "polygamous" panicle with male, female, and herbaceous flowers in the same cluster. However, in practice, the simplest classification is the distinction between male, female, and herbaceous panicles (Batlle and Tous, 1997). In the Ministry's investor guide, it is stated that carob flowers are "multisexual".
The Diversity of Male Types
Male trees also differ within themselves. The two main male types observed in Italy, Portugal and Spain are locally called "red" and "yellow" males according to their spike color. However, it is reported that this feature is insufficient for classification, and red males take longer to bloom than yellow males (Batlle and Tous, 1997).
Nectar and Scent Differences Between Flowers
All three types of flowers secrete nectar. In evaluations based on studies in Spain, it is reported that female flowers are richer than males in terms of both nectar volume and sugar content (Batlle and Tous, 1997). On the other hand, in a study conducted in Jordan and published in Uludağ Beekeeping Journal, it was found that male trees produce more and denser nectar than females (Maha and Haddad, 2012). This difference shows that nectar production may vary according to the variety, region and measurement method.
Male and herbaceous flowers emit a distinctive heavy odor that attracts insects. In an analysis of floral scents in Portugal, more than 25 volatile compounds were identified; female flowers had a greater variety of volatile compounds than male and herbaceous flowers, and the amount of main compounds was lower. The main source of the odor was determined to be the nectar disc in all three flower types (Custódio et al., 2006).
Characteristics of Male, Female and Male Trees
In terms of gardening and landscaping, the function of the three tree types is different from each other.
| Feature | Male tree | Female tree | Hermaphroditic tree |
|---|---|---|---|
| Does it give pods? | Nope | Yes, if it gets dusty | Yes |
| Does it produce pollen? | Yes | Nope | Yes |
| Role in the garden | Pollinator | Main manufacturer | Pollinator and limited producer |
| Flowering time | Relatively short | Long | Long |
Female Trees
The main producer trees of commercial carob orchards are female varieties. The IPGRI monograph states that breeders have preferred female trees to herbaceous because they have produced better pods throughout history, and that the most common varieties in commercial gardens are female. The bulk of the major varieties evaluated in the monograph are female; for example, Spain's 'Negra', 'Rojal', 'Matalafera', Portugal's 'Mulata', 'Galhosa' and Cyprus' 'Tylliria' are classified as female.
Female flowers have a long flowering period. According to phenology studies conducted in Spain, the development of clusters in female and herbaceous varieties takes two months or longer, while this period is 1–1.5 months in males (Batlle and Tous, 1997).
Male Trees
Male trees do not produce pods; therefore, it seems "inefficient" in terms of production alone. However, it is the main source of pollen required for female trees to bear fruit. The World Agroforestry Centre database records that male trees are preferred as ornamental trees because they do not shed pods (Orwa et al., 2009). In urban landscaping, choosing male trees in places where it is not desirable to pour pods on sidewalks is therefore a practical solution.
Hermaphrodite Trees
Hermaphrodites both produce pollen and can produce pods. The IPGRI monograph emphasizes that hermaphrodites are never the main producers in the garden, but attract attention as pollinators. In Italy, types such as 'Bonifacio' and 'Tantillo' were selected for this purpose, while hermaphroditic varieties such as 'Santa Fe' and 'Clifford' grown in California were shown among the promising pollinators. It has also been observed that hermaphroditic types usually bear fruit earlier (in the 2nd–3rd year) than female varieties after grafting (Batlle and Tous, 1997).
Another advantage of hermaphrodites is the flowering time. Since male trees have a shorter flowering period, hermaphroditic pollinators are generally more successful in overlapping with long-flowering female varieties. However, in the monograph, it is stated that hermauded varieties have a special value if they are self-fertile or compatible with females, and this issue has not been sufficiently researched.
Male-to-female ratio in natural populations
In self-growing carob communities, the ratio of male and female trees is roughly equal. In the IPGRI monograph, based on an observation dated 1919, it is stated that about half of the natural trees are male and that there are very few (about 1 percent) of herbels (Batlle and Tous, 1997).
The frequency of herbaceous trees varies from region to region. While female and male types are common on the Mediterranean coast of Spain, herbaceous are rare; heralds are more common on the east coast than in the south and in the Algarve region of Portugal, while the frequency is higher in the Balearic Islands than in the Iberian Peninsula.
An important point is this: Since predominantly female varieties are grafted in gardens propagated by grafting, the male-female balance of a production region may change over time (Batlle and Tous, 1997). In other words, the ratio of half in the natural population is not valid in cultural gardens.
Can Gender Be Understood from Seedlings?
Whether a carob seedling grown from seed will be male or female can only be understood with certainty when the tree blooms. For this reason, about half of the ungrafted trees grown from seed are expected to grow male. In a small experiment published in Australia in 1989, it was tried to predict the sex by treating the branch sections of young seedlings with paint, but the author emphasized that the results should be confirmed when the trees bloom (Hart, 1989).
Studies on gender determination at the scientific level are also ongoing. In a gene expression study conducted in carob flowers, it was observed that the expression levels of some genes associated with the ethylene pathway were directly related to masculinity and it was suggested that ethylene may play a role in sex expression (Caruso et al., 2008). However, these findings have not yet turned into a practical sex test that can be used in the garden.
How many male trees should there be in the garden?
The ratio of pollinator trees in the carob orchard is one of the decisions that directly affects the yield. However, there is no single "right ratio" in the sources.
- The IPGRI monograph states that the recommended rates range from 4 percent to 20 percent; about 12 percent of pollinator trees (i.e. 1 male or hermad to 8 females) appear to be sufficient (Batlle and Tous, 1997).
- In the same source, it is recommended to plant pollinators every three rows and between two female trees in rows, and to place additional male trees in the side rows in the direction of the prevailing wind.
- In Julia Morton's "Fruits of Warm Climates", it is mentioned that one male tree should be planted for every 25-30 female trees (Morton, 1987).
- A recent study of 20 orchards in Mallorca showed that total orchard production peaks when the proportion of male trees is around 25–30 percent (Gómez-Martínez et al., 2025).
The details of the Mallorca study are also noteworthy. The increase in the male-to-female ratio increased the total number of pollinating insects; fruit and seed production per female tree peaked at approximately 0.7 males/females. However, seed weight, the most valuable trait for the farmer, decreased as the male ratio increased. The researchers explain this by the balance between the number of seeds the tree carries and the size of the seed (Gómez-Martínez et al., 2025). These results indicate that the male tree ratio cannot be determined solely by the logic of "the more, the better."
Appropriate ratio; It depends on the wind and insect activity of the region, the flowering times of the varieties used and the germination power of the pollen. The IPGRI monograph also clearly states that the optimum pollinator density and the differences between male and female use have not yet been determined definitively.
The Effect of Pollinator Tree on Yield
In carob, pods do not develop without fertilization. The IPGRI monograph states that all pods contain seeds, and that the pods do not reach their full width in the sections that are missing seeds, indicating that pollination is mandatory. In the same source, it is stated that crop losses due to lack of pollination have been reported in Crete, and that the traditional neglect of the arrangement of pollinator trees may have contributed to low yields and even the abandonment of some groves.
A study conducted in Cyprus also demonstrated the importance of insect pollination in numbers. Compared to flowers whose clusters were covered with a mesh bag and left only for wind pollination, 4 to 16 times more pods were formed in exposed flowers, depending on the region; these pods were heavier, longer and more seeded (Varnava et al., 2023). In short, the presence of a pollen source near the female tree and insects that will carry this pollen affects both the quantity and quality of the product.
Practical Solutions to the Male Tree Problem
In the Mediterranean, growers have used grafting for centuries to prevent planting male trees from taking up space. In the IPGRI monograph, traditional methods are summarized as follows:
- If the rootstock is male, a male branch belonging to the rootstock is left in the middle of the grafted female tree.
- If the rootstock is female, a male or hermit eye is grafted onto the tree.
- In existing gardens with pollination problems, some female trees can be grafted with male or male scions with top grafting.
Morton also states that in Southern Europe, instead of planting separate male trees, male branches are grafted onto some female trees. On the other hand, since about half of the natural trees are male, male trees that grow spontaneously on the roadsides or maquis around the garden can contribute to pollination; however, according to the IPGRI monograph, their number is usually not sufficient.
Grafting male or unproductive wild trees and transforming them into productive varieties is another issue. We discuss these methods in our article "Grafting Techniques in Carob Tree".
Frequently Asked Questions
Does a male carob tree bear fruit? Male trees only produce pollen and do not form pods. Pods occur in female and male trees.
My carob tree is blooming but not bearing fruit, why? The tree may be male or female, but there may not be enough pollen sources around it. Rainy and windy weather during the flowering period, lack of insect activity and periodicity can also reduce fruit set.
How many male trees should there be in a garden? Sources give rates ranging from 4 percent to 30 percent. The IPGRI monograph found a ratio of around 12 percent (1 pollinator to 8 females) sufficient, while a recent study in Mallorca found the total production highest at 25–30 percent males.
Can gender be understood during the seedling period? There is no reliable and widely used method. The gender is precisely understood when the tree blooms; therefore, productive gardens are established with grafted saplings.
From Carob Orchard to Product with Carob Türkiye
The balance of male, female and male trees in carob directly affects the amount of pods and seeds to be taken from the garden. Establishing this balance correctly is the first step in obtaining both fruit flesh and valuable seeds efficiently.
At Carob Türkiye, we supply carob fruit, crumbs, flour/powder, seeds, and extracts. Our Products Carob Fruit and Carob Seed You can examine the importance of the kernel What is Carob Seed? You can read it in our article. For your wholesale and export requests Contact Now You can contact us on our page.
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handle. net/ 11452/ 15871 Foreign sources
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