What trees reproduce asexually? There are 2 types of trees: gymnosperms any woody plant that doesn't have a flower and angiosperms any flowering plant. Trees can reproduce asexually by budding their cells are totipotent, and so one "cut" of a tree can grow into a whole organism. Pine trees have both male cones and female cones. Are oak trees Monoecious? Oaks and many other trees are monoecious.
Potentially, every tree of reproductive age is capable of producing acorns, and the majority of female flowers are pollinated by the male flowers of other oak trees within the same area.
In contrast, other trees, such as persimmon and white ash, are dioecious. How long do live oaks drop pollen? How does an oak tree grow from an acorn? If left unmolested, the seedling will gradually grow and develop into a sapling tree after four to five years. The sapling then grows into a small tree that flowers and produces its own acorns. Many oak trees can live for hundreds of years, fruiting new acorns every spring and summer. Where do oak trees grow best? You can find an oak tree for almost all of the planting zones in the United States.
Mid-April is usually when the pollen is at its worst, especially for people who have allergy problems anyway. One of the reasons why pollen is so bad for people prone to allergies is because the grains are very tiny; therefore, they are easily inhaled and super easy to spread.
Nevertheless, as far as oak tree reproduction goes, this is what has to happen in order to pollinate the trees. Once an oak tree gets here, though, it fortunately stays here for a very long time! In most cases, wind pollination occurs and pollen is deposited on another tree. Oak tree branch acorn nut image by Yay. Some Final Remarks. All pollinations were performed by JHW. Pollen applications were practiced beforehand and the number of grains counted until a consistent dosage level was attained.
Flower or fruit abortion is episodic in oaks and occurs during several distinct developmental stages Table 1 : during floral development pollination period , during ovule development and pollen tube growth period 1 , and during formation of the endosperm and early embryo period 2; Feret et al. After embryo growth begins period 3 , abortion is negligible and is often associated with herbivore damage Williamson, A final period of maturation ends when the acorn falls from the tree period 4.
Differentiation between prezygotic period 1 and postzygotic periods 2—4 phenomena were determined by monitoring the success of crosses from pollination to maturity. For statistical analyses, fruit survival at SP1, SP2 and SP3 was calculated as the number of nonaborted fruits remaining divided by the number of flowers pollinated.
At SP4, survival fruit set was calculated as the number of nonabortive acorns that fell into protective screens, divided by the number of flowers pollinated. Non-abortive acorns were characterized by embryo swelling extending above the cupule rim.
The experimental pollinations followed a full diallel cross at each site. Instead, the main interest was in differences in patterns of reproductive success in two different ecological settings.
Thus, a nested, mixed-model ANOVA was used with site, species, cross-type, and pollen dose as fixed effects; trees nested within site and species, and branches nested within trees error term , as random effects. Models were constructed to examine variation in female and male function separately. The components of female function were analysed separately. Character index scores of Q. Scores of Q. The character index scores of the 16 study trees are listed in Table 2.
Most of the Q. The exceptions were Q. Six of the eight Q. Male reproductive effort, as measured by catkin production, was consistently high in Q. These same trees were among the highest female flower producers Table 3. At HZ, the pattern of high pollen production by Q. Many Q. Fruit survival at the end of period 1 SP1 differed significantly between species Table 4. Quercus gambelii had lower overall fruit survival during this time period than did Q.
In both species, fruits resulting from conspecific and heterospecific fertilizations survived with equal frequency Fig. In contrast, self-crosses survived differently than nonself crosses. Percent fruit survival 6 weeks after pollination SP1. The final factor to have a significant effect on fruit survival during period 1 was trees Table 4.
This finding indicates there was variation in fruit survival among individual trees. Site and dose did not influence fruit survival, nor were any other interactions significant Table 4. Only 3. Therefore, rather than evaluating fruit survival at SP2, 3 and 4 separately, only the data from SP4 is reported, recognizing that these results occurred during period 2.
The effect of dose, both as a main effect and in all interactions, was also nonsignificant Table 5. Cross type was significant both as a main effect and in all interactions other than dose Fig. In general, conspecific outcrosses were more successful than self- and heterospecific crosses. In contrast, Q. Thus, when Q. This pattern of variation suggests that Q. The reproductive success RS of Q. At HZ, Q. Quercus grisea had equivalent reproductive success at both sites for each cross type.
In contrast, the conspecific cross type of Q. One possible explanation for this outcome is stress. Quercus gambelii is a northerly distributed, mesic habitat species, that may be under considerable stress at the HZ site. At this site, representatives of Q. It is likely that Q. Environmental stress can affect sexual reproduction through a reduction of male or female function, or both Freeman et al. The results reported here suggest that a reduction in male function is responsible for the poor reproductive success of conspecific pollinations of HZ Q.
Female function is less implicated as a factor in this result because heterospecific fruit set of HZ Q. Another indication of poor male function was the very low pollen production of HZ Q.
Low pollen production can be associated with low pollen vigour Schlichting, ; Schoper et al. Female flower production, conversely, was not low in Q. Thus, factors associated with male performance appear to play a stronger role than those associated with female performance in causing low conspecific outcrossing success of HZ Q. In light of this conclusion, it might be argued that the Q. This argument is not supported by the RAPD analysis.
Moreover, Q. In addition, the pollen of this tree had nonzero siring success on all other females, conspecific or heterospecific. Finally, the lack of a pollen dose effect suggests that reduced male function was not due to a reduction in the number of viable pollen grains produced, which might be expected if introgression had led to disturbed meiosis.
Thus, introgression does not appear to explain the reduction in male function observed among Q. One effect of decreased male function in Q. Thus, one explanation for the increased frequency of hybrids at the HZ site is poor pollen quality in Q.
Poor pollen quality also reduces pollen competitive ability, and pollen competition can be an important arbiter of species boundaries in other wind-pollinated tree species Williams et al. An obvious, but untested, prediction of this hypothesis is that most of the hybrids at this site should harbour Q. There is also evidence of asymmetric cross-compatibility between oak species Aas, ; Steinhoff, At least one study has sought to explain such patterns through a combination of ecological, demographic and reproductive factors, including male function Petit et al.
This study offers a new explanation for both variation in hybrid zone formation as well as for why such zones often display asymmetric patterns of hybridization, although these data cannot be viewed as a test of the environmental emasculation hypothesis. A test of the hypothesis would require zones of sympatry both with and without significant hybridization to be the experimental units, and the present experimental design had no replication at the level of zones of sympatry.
The discovery that the most successful producer of pollen and fruits among the Q. Many long-lived perennials, including oaks, produce far more flowers than mature fruits Stephenson, Both species had substantial flower abortion prior to fertilization Q.
Importantly, these abortions were random with respect to cross type, and suggest an early maternal adjustment to resource availability Lloyd, Mate discrimination in white oaks appears to be a consequence of postzygotic processes.
Self-pollinated flowers aborted at the same rate as conspecific and heterospecific flowers before fertilization period 1 , but were nearly completely eliminated after fertilization during period 2.
In addition, the low heterospecific RS seen in both species also occurred during period 2, as well as the dramatic reduction in Q. Almost no abortions occurred during acorn growth and maturation periods 3 and 4.
This pattern suggests mate recognition occurs via postzygotic mechanisms, such as late-acting incompatibility and inbreeding or outbreeding depression, but not by prezygotic self or hetero specific incompatibility.
The abortion peak late in period 2 corresponds to the period when the early embryo first undergoes differentiation. Wiens et al.
Poor pollen quality may also lead to increased embryo abortion. For example, slower pollen tube growth may result in delayed fertilization, leading to developmental selection amongst embryos Buchholz, It has been shown in other flowering plants, such as Phaseolus spp.
An alternative interpretation of the high abortion rate in period 2 is that these abortions represent unfertilized flowers which aborted late. This interpretation seems unlikely, for several reasons. First, ample time was allowed for crosses that could not fertilize eggs to express signs of abortion.
In fact, during period 1, discrimination between self and nonself was expressed through differential flower abortion Fig.
Second, almost all abortions recorded at SP1 were flowers that had already fallen, rather than flowers that were turning brown J. Williams, pers. This indicates that SP1 occurred well after an earlier abortion peak.
In contrast, at SP2 many aborted fruits were still on the tree i. This indicates that the second abortion peak occurred late in period 2. Thus, if the abortions which occurred during period 2 were due to lack of fertilization, the delay of any sign of impending abortion was approximately 4—6 weeks long. Heterospecific pollen swamping of isolated plants has been implicated in the production of hybrids in nature e. Arnold et al.
If variation exists for pollen tube growth rate or vigour, then increasing the amount of heterospecific pollen on a stigma might be expected to increase the probability of fertilization. In fact, neither conspecific or heterospecific fertilization increased when pollen loads were increased from approximately 9— pollen grains. This is further evidence for a lack of strong pre-fertilization barriers in these species, at least when heterospecific pollen occurs alone on a stigma.
Whether conspecific pollen outcompetes heterospecific pollen for fertilizations when both types of pollen occur on a stigma awaits further study. In oaks and many other groups of species, the level of reproductive isolation between closely related species varies geographically.
By comparing characteristics of individuals from areas with different levels of reproductive isolation it becomes possible to pinpoint factors that mediate reproductive isolation. The results of this study indicate that marginal habitats can increase the probability of hybrid offspring formation by altering the quantity and quality of male gametes environmental emasculation of one parental species.
Aas, G. Kreuzungsversuche mit Stiel-und Traubeneichen Quercus robur L. Allg Forst-Jagdz , : — Google Scholar. Aizen, M. Flowering-shoot defoliation affects pollen grain size and postpollination pollen performance in Alstroemeria aurea. Ecology , 79 : — Article Google Scholar. Anderson, E. Hybridization of the habitat. Evolution , 2 : 1—9. Arnold, M. Natural Hybridization and Evolution. Oxford University Press, Oxford.
Oak trees produce both male and female flowers on the tips of their uppermost branches, which are relatively unnoticed. Pollen from the male flower fertilizes the female ovary, which develops into an acorn. The petals and sepals of the ovary fuse to form the acorn's top, or cap.
The acorn falls off the tree in late summer or early fall, and under the right conditions will germinate and grow into a new oak seedling. Like other deciduous trees that lose their leaves each fall, oaks go through a dormant period during the winter.
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