The expression of gender and sex in plants is a highly intricate process that has been the focus of numerous research studies, which are still ongoing today. Both angiosperms and gymnosperms have been studied in relation to their gender expression. Plants can be classified as male, female, hermaphroditic, or monoecious, depending on their reproductive characteristics. However, gender or sex in plants is not a straight forward categorization, but rather a quantitative trait that is influenced by a variety of internal and external factors. These factors include complex mating strategies, environmental factors and the reproductive biology of the plants. As a result, categorizing plants based on gender or sex can be limited and may not fully capture the complexity of their reproductive biology. (Lloyd.,1980).
To comprehend the ecology of long-lived trees and the pressures that influence their fitness, a thorough investigation of their reproductive patterns is important (Harper.,1977). While there is less research on the life cycle of trees, particularly gymnosperms those grow in undisturbed forests, there is convincing literature available on the seed masting phenomenon that occurs in many angiosperms and some gymnosperms, particularly tree species in temperate forests (Harper., 1977; Silvertown., 1980; Ogden., 1985; Norton & Kelly., 1988). Examining gender expression patterns in plants has aided evolutionary biologists in comprehending and assessing the mechanisms behind plant breeding systems and their assessment. Gender expression is vital in determining the genetic contribution of plants as either male or female (Lloyd., 1979). Various factors, such as size, growth rate, mortality, light, and nutrient resources, can impact the ontogenic sex change in plant species (Heslop-Harrison., 1957; Charnov and Bull., 1977; Freeman., 1980; Schlessman., 1986; Korpelainen., 1998; De Jong and Klinkhamer., 2005). Resource-dependent gender plasticity is typically observed in natural plant populations, which ultimately helps to maintain gender dimorphism (Delph and Wolf., 2005). According to reports, unisexual flowers in angiosperms have evolved from ancestral hermaphrodite flowers (Renner and Ricklef., 1995, Mitchell and Diggle., 2005). This evolution may have occurred through two potential ways, either via monoecious or gynodioecious plants or via reverse mutation of dioecious plants that regained male function after losing female function (Barret., 2002). Genetically dimorphic breeding systems such as gynodioecy (a population with females and hermaphrodites), androdioecy (a population with males and hermaphrodites), and dioecy (a population with males and females) exist in plants, with one genetic dimorph typically functioning more as a female while the other functions more as a male (Delph and Wolf., 2005). Studies on gender dimorphism have played a crucial role in understanding the evolutionary forces that influence genetic variation. Dioecy is relatively rare in the plant kingdom, with only 6% of plants being dioecious (Renner and Ricklefs., 1995). Dioecy is believed to have evolved from either monoecy or gynodioecy, while monoecy may have evolved from dioecy, as seen in the Momordica genus, where it has likely occurred seven times (Charlesworth and Charlesworth., 1978; Renner and Won., 2001; Barrett., 2002; Schaefer and Renner., 2010).
It has been reported that dioecy in gymnosperms has evolved from monoecy, with the Pinopsida group being a notable example where this has occurred 10–13 times (Leslie et.al., 2013). Despite monoecy being more common in angiosperms, dioecy is actually more dominant in gymnosperms (Charnov., 1982), with the majority of Cycadales, Ginkgoales, and Gnetales species being dioecious, while conifers are predominantly monoecious (Owens et. al., 1990). However, there is uncertainty in the behavior of some species and genera, and there are reports of plasticity in which species can change from monoecious to dioecious or vice versa (Vasek., 1966). Some species also switch between male and female phases from season to season. This phenomenon is also known as diphasy. Diphasic plants suppress one or the other sex in entire season probably by arresting male or female function in flower primordia. Several studies have explored the factors that influence sex expression in gymnosperms such as age, position of strobili on the plant or shoot, growth hormones, and environmental factors in Ginkgo biloba, Ephedra Sps, Abies Sps, and Pinus Sps (Lee., 1954; Newcomer., 1954; Mehra., 1950; Wheeler et. al., 1982). However, the relationship between sex expression and the physiology of gymnosperms is not well understood.
Conifers are most studied gymnosperms and their reproductive cycle is mostly dependent upon the environmental factors, age of the plant, temperature, weather, growth hormones, branching patterns, exposure to sunlight and nutrition. Conifers are among the oldest extant seed plant lineages and their reproductive biology hold clues about seed plant evolution. The earliest fossil records dates back conifers to the carboniferous period (300 million years ago), possibly arising from chordiates, which is a genus of seed bearing gondwanan plants with cone like fertile structures. Conifers were the most dominant land plants of Mesozoic era. The massive, catastrophic evolutionary events taking place at Palaeozoic era wiped out a large number of conifers of that time. Only a few species managed to adapt and survive till this date among which most of them are large, vascular, seed bearing land plants with cone like fertile structures belonging to the division Pinophyta. They have evolved and acquired some important features in order to survive extinction like, less dependency on water, heterospory, winged pollens and others (Williams., 2009). One of the characteristic feature acquired by conifers is iteroparity i.e., recurrent production of seeds (Williams., 2009). Cedrus deodara is among the long lived conifers which are diplohaplontic, iteoparous, coniferous evergreen trees belonging to the family Pinnaceae. Commonly known as Himalayan cedar or deodar and native to western Himalayas in Eastern Afghanistan, Northern Pakistan, South Western Tibet, Western Nepal and India (Jammu and Kashmir, Himachal Prdadesh, Uttarakhand, Sikkim and Arunachal Pradesh). Cedrus deodara (Himalayan cedar) is one of the most important conifer, commonly known as deodar, is indigenous to India (Dallimore and Jackson., 1996) and occurs throughout the temperate regions of Western Himalayas predominantly between 1750m to 2500m, 15ºW and 80ºE and 30º-40ºN Chaney., 1993: Demecti., 1986: Maheshwari and Biswas., 1970). Every year Cedrus deodara completes its reproductive cycle e(Farjon., 1990,ither by producing a new set of reproductive organs or they do not produce any reproductive organs at all. It tends to remain in their vegetative state only. Therefore they have a good seed year once in every three to four years. Such disparity in the reproductive development of conifers has never been understood clearly hence it provides a grey area for research and Cedrus deodara has been chosen as a potential tree to carry out research in this area.