The botanical term parthenocarpy refers to the development of the ovary of a flower into a fruit without fertilization. [The biological term parthenogenesis refers to the development of an egg without fertilization.] Fruits that develop parthenocarpically are typically seedless. Some seedless fruits come from sterile triploid plants, with three sets of chromosomes rather than two. The triploid seeds are obtained by crossing a fertile tetraploid (4n) plant with a diploid (2n) plant. When you buy seedless watermelon seeds, you get two kinds of seeds, one for the fertile diploid plant and one for the sterile triploid. The triploid seeds are larger, and both types of seeds are planted in the same vicinity. Male flowers of the diploid plant provide the pollen which pollinates (but does not fertilize) the sterile triploid plant. The act of pollination induces fruit development without fertilization, thus the triploid watermelon fruits develop parthenocarpically and are seedless. Most bananas purchased at your local supermarket came from sterile triploid hybrids. The fruits developed parthenocarpically and are seedless.

The cultivated banana is often listed in botanical references as Musa x paradisiaca (Musaceae), although it is actually a complex hybrid derived from two diploid Asian species, M. acuminata and M. balbisiana. Common cultivated bananas are usually triploid (3n) with three sets of chromosomes. [Note: The word "set" is defined here as one haploid set of chromosomes.] If A represents one haploid set of chromosomes from diploid M. acuminata (AA) and B represents one haploid set of chromosomes from diploid M. balbisiana (BB), then hybrid bananas have three sets of chromosomes represented by AAB, ABB or another 3-letter (triploid) combination of A's and B's. Like seedless watermelons and red grapes, bananas are sterile and do not produce mature seeds. [Sometimes you can find aborted ovules inside the fruit that appear like tiny black dots.]

In the formation of gametes during normal meiosis, homologous chromosomes must pair up with each other during synapsis of prophase I. Like other odd polyploids (with 3 sets of chromosomes), bananas are sterile and seedless because one set of chromosomes (A or B) has no homologous set to pair up with during synapsis of meiosis. Therefore meiosis does not proceed normally, and viable gametes (sex cells) are not produced. Since banana fruits (technically berrylike ripened ovaries) develop without fertilization they are termed parthenocarpic. Without viable seeds, banana plants must be propagated vegetatively (asexually) by planting corms, pieces of corms or sucker sprouts.

Parthenocarpy can be induced by growth hormones such as gibberellic acid (GA₃) in which the ovaries mature without fertilization. Grape cultivars such as 'Thompson Seedless' are treated with gibberellic acid to order to produce larger fruits with longer internodes. The bunches have wider spaces between the grapes and better air circulation, reducing their susceptibility to fungal diseases and rotting within the bunch. Contrary to some references, 'Thompson Seedless' grapes are not parthenocarpic because fertilization does occur, but the ovules fail to develop into seeds within the maturing fruit.

In cultivated figs, parthenocarpy generally refers to the development of the ovaries of female flowers within the syconium into drupelets without fertilization. The syconium is the structure that you typically associate with an edible fig fruit; however, it is really a flask-shaped structure lined on the inside with numerous unisexual flowers. The actual botanical fruits (called drupelets) develop within the syconium. Since the entire syconium enlarges and ripens into a juicy, sweet morsel, it is often referred to as a fruit. The female flowers are pollinated by a tiny female fig wasp that enters the syconium through a pore called the ostiole. According to W.B. Storey (Advances in Fruit Breeding, 1975), there are 2 genetically determined forms of parthenocarpy: stimulative and vegetative. Stimulative parthenocarpy involves the insertion of the wasp's ovipositor down the stylar canal into the ovary of short style flowers. It can also be induced by blowing air into the syconium, or by spraying the syconium with a plant growth regulator. The mature drupelets may contain a wasp (if an egg was laid in the ovary) or it may be empty. Vegetative parthenocarpy involves the formation of drupelets without any external stimulation, and is responsible for the hollow drupelets inside common figs such as "black mission," "kadota," and "brown turkey." [Some authors use the term parthenocarpy to describe the ripening of seedless fig syconia on the tree without any pollination or fertilization.]

The mule is a hybrid between a female horse or mare (2n=64) and a male donkey or jackass (2n=62). Since the mare contributes 32 chromosomes in her egg and the jackass contributes 31 chromosomes in his sperm, the mule has a diploid number of 63. Male and female mules are typically sterile because the horse and donkey chromosomes differ in number and they are not homologous. Therefore, the horse and donkey chromosome doublets fail to properly pair up with each other during synapsis of meiosis I. In fact, one horse doublet lacks a donkey doublet to pair up with. By the way, if the mother is a donkey or jennyass and the father is a stallion, the resulting sterile hybrid is called a hinny.

The mule is an unusual animal because it has an odd number of chromosomes (2n=63) that is not divisible by two. The haploid number of a mule is not 31.5 because you can't have half of a chromosome in the gametes. But there is another way to get an animal or plant with an odd number of chromosomes called aneuploidy. If the chromosome number in the sperm or egg is more or less than the normal number of chromosomes in a haploid set, the resulting offspring (called an aneuploid) may have a chromosome number that is not exactly diploid (2n). Trisomy (2n+1) occurs when an individual has an extra copy of a chromosome. Examples of trisomy in people are Down's syndrome (three #21 chromosomes) and several sex chromosome aneuploidies caused by extra X or Y chromosomes, including Klinefelter's Syndrome (XXY), Trisomy X Syndrome (XXX) and the XYY Male Syndrome (XYY). Monosomy (2n-1) is caused by an individual missing one chromosome. Turner's Syndrome is a human female who received only one X chromosome from one parent and no X or Y chromosome from the other parent. Usually the cause of aneuploidy is nondisjunction during meiosis I or meiosis II, in which the sperm or egg carries extra or fewer chromosomes. In animals, autosomal monosomies and trisomies (abnormal numbers of autosomes) are usually detrimental and often fatal. In duckweeds (Family Lemnaceae), Mr. Wolffia's favorite plant family, the number of chromosomes in one haploid (1n) set is 10; however, polyploidy is common in the family, including 3n=30, 4n=40, 5n=50, 6n=60, 7n=70, and 8n=80. There are also good examples of aneuploidy in the duckweeds Landoltia punctata, Lemna minuta and L. minor, including adult (sporophyte) individuals with 36, 42, 43 and 44 chromosomes. Aneuploid duckweeds often lack vigor and are sterile. Odd polyploids such as 3n, 5n and 7n are also sterile. Can you guess why?

According to John Roach (National Geographic News 16 May 2006), DNA evidence confirms a natural hybrid between a female polar bear and a male grizzly. Apparently, grizzly bears have migrated north into Canada's western Arctic, and occasionally enter the range of polar bears. The male hybrid's white fur was interspersed with brown patches. It also had long claws, a concave facial profile, and a humped back--all grizzly characteristics. Unfortunately, this unique hybrid bear was killed by a hunter who thought it was a polar bear when he pulled the trigger. The common name for this hybrid is "polargrizz." I have not substantiated this remarkable discovery in a peer-reviewd scientific journal.

The citrus family (Rutaceae) contains some of the world's most delicious fruits, including numerous hybrid crosses between species. The popular tangelo grown in San Diego County is a hybrid produced by crossing a grapefruit (C. x paradisi) with a tangerine (C. reticulata). The grapefruit is sometimes called a pomelo, and this explains the blending (portmanteau word) of tangerine and pomelo. Actually, the grapefruit is a hybrid produced by crossing the shaddock or pummelo (Citrus maxima) with a sweet orange (C. sinensis). The shaddock is a large, thick-skinned, tropical citrus fruit up to six inches (15 cm) in diameter that is occasionally sold in supermarkets.

According to Apples: A Catalog of International Varieties by Tom Burford, there are 17,000 varieties of apples! Most of the apples grown commercially are probably diploid (2n), although there are many triploid varieties. For example, 'Gravenstein' apples are triploid with a chromosome number of 51 (3n=51). They are produced by the union of a diploid egg (2n=34) and a haploid sperm (n=17). This is accomplished by crossing a tetraploid plant (4n=68) with an ordinary diploid plant (2n=34). Because the triploid (3n) varieties are sterile, they must be propagated by grafting, where the scions of choice cultivars are grafted to hardy, pest-resistant root stalks.

Apples are mentioned throughout most of recorded human history. The generic name Malus is derived from the Latin word malus or bad, referring to Eve picking an apple in the Garden of Eden; however, some biblical scholars think the fig, and not the apple, was the forbidden fruit picked by Eve. One of the earliest records of any fruit eaten by people of the Middle East is the common fig (Ficus carica). Remnants of figs have been found in archeological excavations dating back to the Neolithic era, about 1000 years before Moses. The fig is also the first tree mentioned in the Bible in the story of Adam and Eve. There are some scholars who think the apricot is a more likely candidate because it was an abundant fruit (along with figs) in the ancient Palestine area. Other interesting tales about apples include Johnny Appleseed, William Tell, Sir Isaac Newton, and Apple Computers.

The rose family (Rosaceae) includes many economically-important fruit trees known as stone fruits in the genus Prunus. Each species has many vamed cultivated varieties (cultivars). Botanists have moved some of these species into separate genera, including Amygdalus (peach) and Armeniaca (apricot). Some examples of stone fruits are fuzzy-skinned peaches (P. persica syn. Amygdalus persica), smooth-skinned peaches called nectarines (another variety of P. persica), plums (P. domestica), apricots (P. armeniaca syn. Armeniaca vulgaris), and cherries (P. avium and P. cerasus). Like apples and pears, there are hundreds of cultivated varieties. These fruits are technically referred to as drupes because they consist of an outer skin or exocarp, a thick, fleshy middle layer or mesocarp, and a hard, woody layer (endocarp) surrounding the seed. The part of these fruits that is eaten by people is the mesocarp layer and also the exocarp if you don't bother to peel them. The woody endocarp layer protects the seed and probably aids in the dispersal of drupaceous fruits by hungry herbivores. In wild plants with drupes, the seeds can pass through the entire digestive system of grazing animals and be planted in new locations. The almond (Prunus amygdalus syn. Amygdalus communis) is also a drupe with a green exocarp and thin mesocarp surrounding the pit. When you crack open an almond to get the seed, you are actually cracking open the endocarp layer.

Some species of Prunus have been artificially crossed to produce some unusual hybrids. The peachcot (Prunus persica x P. armeniaca) is a hybrid between the peach and apricot; the cherrycot (P. besseyi x P. armeniaca) is a hybrid between the cherry and apricot; the plumcot (P. domestica x P. armeniaca) is a hybrid between the plum and apricot. Some of these hybrids have many different named cultivars, depending on which varieties of stone fruits have been crossed together. In addition, hybrids often retain more characteristics of one parent and are given special names. For example, some cultivars of plumcots are called "pluots" because these resemble plums more than apricots. Plumcots called "apriums" resemble apricots more than plums.

Modern varieties of the watermelon are derived from the native African vine Citrullus lanatus (syn. C. vulgaris). Cultivated for thousands of years in the Nile Valley, this species still grows wild in the arid interior where it supplies native people with water during drought seasons.

According to R.W. Robinson and D.S. Decker-Walters (Cucurbits 1997), wild populations of C. lanatus var. citroides, which are common in central Africa, probably gave rise to domesticated watermelons (var. lanatus). Wild, ancestral watermelons (var. citroides) have a spherical, striped fruit, and white, slightly bitter or bland flesh. The pale flesh tastes like the rind of a typical watermelon. They are commonly known as the citron or citron melon, not to be confused with the "citron" Citrus medica of the Citrus Family (Rutaceae). The citron is also called "preserving melon" because the fruit rind is used in preserves, jellies and to make pickles or conserves. Because of its high pectin content, it is added to fruit juices to make them jell more rapidly. One plant may produce up to 100 fruits, which are commonly fed to livestock. Citron melons become weedy vines in cultivated melon fields of North America, and are unmistakable among other cucurbits because of their pinnatifid (pinnately dissected) leaves. The citron is naturalized in the Cape Region of Baja California, along with the curious teasel gourd.

Modern triploid watermelons (with three haploid sets of chromosomes) are unable to produce viable gametes during meiosis, and much to the delight of growers, their ripened melons are seedless. [Note: The word "set" is defined here as one haploid set of chromosomes.] They are produced by crossing a tetraploid (4n) seed parent bearing 2n eggs with a diploid (2n) pollen parent bearing haploid (n) sperm. Tetraploid plants are produced by treating the terminal buds of diploid plants with colchicine, causing the chromosome number of the meristematic cells inside to double. The haploid (n) sperm from a pollen grain from the male flower of the 2n parent fertilizes the diploid (2n) egg inside the ovule of a female flower on the 4n parent. The resulting 3n zygote develops into a 3n embryo inside a seed. Planting this seed will yield a 3n watermelon plant bearing 3n seedless watermelons. The following illustration shows this cross resulting in a triploid watermelon plant:

The triploid seed will germinate and grow into a triploid plant bearing triploid male and female flowers, but the flowers will not produce viable sperm-bearing pollen or eggs because of the odd number of chromosome sets (3). With three sets of chromosomes, one set will not have a matching (homologous) set to pair up with during synapsis of prophase 1 of meiosis. This synaptic failure results in gametes that are not viable, therefore double fertilization inside the ovule does not occur and an embryo-bearing seed is not typically formed. When you buy seedless watermelon seeds, you get two kinds of seeds, one for the fertile diploid plant and one for the sterile triploid. The triploid seeds are larger, and both types of seeds are planted in the same vicinity. Male flowers of the diploid plant provide the pollen which pollinates (but does not fertilize) the sterile triploid plant. The act of pollination induces fruit development without fertilization, thus the triploid watermelons are seedless.

The radish (Raphanus sativus) produces a crisp, edible taproot with many varieties, including white & red radishes, and giant oriental radishes 4 feet long and 40 pounds. The wild radish is a very common spring weed in San Diego County. Note: The bigeneric hybrid (Raphanobrassica) or rabbage is a cross between the radish (Raphanus n=9) and cabbage (Brassica n=9). The diploid hybrid has two sets of chromosomes, one set (R) from the radish parent and one set (C) from the cabbage parent. [Note: The word "set" is defined here as one haploid (n) set of chromosomes.] Since each set includes 9 chromosomes, the diploid rabbage has a total of 18 chromosomes. The diploid hybrid (RC) is sterile because the radish and cabbage sets of chromosomes are not completely homologous, and fail to pair up during synapsis of meiosis I. A fertile tetraploid (4n=36) hybrid (RRCC) has also been developed. It produces viable gametes and seeds because the radish chromosomes have another radish set to pair up with (RR), and the cabbage chromosomes have another set to pair up with (CC). Unfortunately this wonder plant has the leaves of the radish and the roots of the cabbage.

Rye (Secale cereale) is a diploid plant (2n) composed of 2 sets of chromosomes (DD), each set with 7 chromosomes (D=7). [Note: The word "set" is defined here as one haploid set of chromosomes.] Therefore, the diploid number, or number of chromosomes in the rye sporophyte (DD), is 14. Bread wheat is a hexaploid (6n) composed of 6 sets of chromosomes (AA, BB & CC), each set with 7 chromosomes (A=7, B=7, C=7). Therefore, the number of chromosomes in the wheat hexaploid sporophyte (AABBCC) is 42. Triticale (Triticosecale) is a bigeneric hybrid between wheat (Triticum aestivum n=21) and rye (Secale cereale n=7). The resulting hybrid (ABCD) contains one set of rye chromosomes (D) and 3 sets of wheat chromosomes (ABC), a total of 28 chromosomes (7 + 21). It is sterile because the rye (D) set has no homologous set to pair up with during synapsis. This sterile hybrid seedling is treated with colchicine to produce a plant with twice as many chromosomes (i.e. 2A's, 2B's, 2C's and 2 D's), a total of 56. The fertile hybrid is an octoploid (8n) because it contains 8 sets of chromosomes. The diploid rye plant (DD) can also be crossed with tetraploid durum wheat (T. turgidum AABB) to produce a sterile triploid hybrid with 3 sets of chromosomes (ABD). This hybrid is treated with colchicine to produce a fertile hexaploid (6n) version of triticale (AABBDD). The following table shows a simplified summary of octoploid and hexaploid versions of triticale.

Durum wheat (Triticum turgidum ) is derived from wild emmer wheat of Syria. Emmer wheat is a tetraploid hybrid (4n=28) between einkorn wheat (T. monococcum or a relative) and a grass similar to the present-day goat grass (T. speltoides = Aegilops speltoides); or possibly T. longissima or T searsii. The original diploid (2n=14) emmer wheat was probably sterile because it contained only 2 sets of chromosomes, one from the einkorn parent (n=7) and one from the goat grass parent (n=7). Through a natural doubling of the chromosomes, a fertile tetraploid emmer wheat with 4 sets of chromosomes was produced. A mutation in the tetraploid emmer wheat, causing the bracts (glumes) enclosing the grain to break away readily, gave rise to the tetraploid durum wheat (T. turgidum or T. turgidum var. durum). The readily detachable grain makes the separation of the grain from the chaff relatively easy and is why durum wheat is called a "free-thrashing" type of wheat.

Tetraploid wheat also contains two proteins that combine to form a tenacious complex called gluten. Because of gluten, the wheat flour becomes elastic when mixed with water and kneaded, and when yeast is added, it rises into firm loaves. Yeast cells in the dough undergo fermentation and release carbon dioxide which becomes trapped in the glutinous protein mass. Baking "sets" the dough by drying the starch and denaturing the gluten protein. As the dough bakes, the carbon dioxide gas expands into larger bubbles, thus producing the porous, spongy texture of bread. Corn does not make good loaves of bread because it lacks gliadin, one of the key proteins of gluten. Consequently, corn bread crumbles and falls apart easily.

Bread wheat (T. aestivum) is also a free-thrashing type of wheat. It is a hexaploid (6n) hybrid, four sets from an emmer wheat parent and two additional sets from a wild, weedy species (T. tauschii = Aegilops squarrosa). The endosperm of this hybrid wheat is especially high in protein and surpasses other wheats for bread making.

The fragrant white Easter lily (Lilium longifolium) is originally from southern Japan and Taiwan. Spectacular tetraploid hybrids of this beautiful lily are grown in greenhouses throughout the world. The white Madonna lily of Europe, depicted in numerous Renaissance paintings of the Annunciation, is Lilium candidum.

The diploid (2n) hybrid between these two species is sterile because the nine C. epilobioides chromosomes and the nine C. unguiculata chromosomes are not truly homologous; therefore, the chromosomes fail to pair up properly during synapsis of Meiosis I. A naturally-occurring, fertile, tetraploid hybrid with four sets of chromosomes (two from each parent) gave rise to a new breeding population of C. delicata, which is considered to be a separate species. The hybrid has 18 chromosomes in its gametes (egg and sperm) and 36 chromosomes in the cells of the sporophyte. The petals lack the long stalk (claw) of C. unguiculata and are somewhat intermediate between the two parents. By the way, clawed mammals are referred to as unguiculates (mammals with hoofs are called ungulates), but in botany the term claw refers to the slender stalk of a petal.

According to T. F. Niehaus (personal communication, 2004), hybrids are encountered where the distribution of two Brodiaea species overlap. The hybrids show a range of intermediate characteristics between the parents. Under controlled greenhouse conditions, Niehaus was able to hybridize every combination between all species and obtain seed. In a few crosses a relatively high percentage of seed set was obtained, although seed set was low in most interspecific crosses. He was able to grow the hybrid seeds to flowering in 2-3 years. According to Niehaus (1971), the majority of hybrids have sterile pollen; however, they can propagate by growing numerous cormlets per plant. Hybrid swarms are a fairly common phenomenon in other genera of flowering plants, including oaks (Quercus), penstemons (Penstemon) and prickly pears (Opuntia).

Niehaus (1971) suggests that Brodiaea polyploids are alloploids (crosses between different species), but then suggests that autoploidy may also be present. In addition, Niehaus states that "no meiotic irregularities or quadrivalents were observed in any polyploids." Normally homologous chromosomes pair up in 2's (bivalent) during synapsis of meiosis I. If homologous chromosomes associate in 4's rather than 2's, this is called a quadrivalent. Quadrivalent chromosome arrangements result in gametes with twice as many chromosomes and polyploids with higher numbers of chromosomes. If brodiaeas do not form quadrivalents, then allopolyploids are formed by adding up the gametophyte chromosome numbers of the two parents. For example, 24 chromosomes from B. terrestris ssp. kernensis plus 12 chromosomes from B. filifolia would result in a polyploid hybrid sporophyte with 36 chromosomes.

One possible explanation for hybrid sterility may be synaptic failure at prophase I of meiosis. Niehaus (1971) studied several populations of "Brodiaea jolonensis" in southern California and published sporophyte chromosome numbers of 36. We are certain that these populations are Coastal BTK and not B. jolonensis. My tentative count for Coastal BTK in San Marcos is also 36. If these populations are hexaploid (6n = 36) with a base number of 6 (n = 6), a cross between a tetraploid (4n) BO (or BT) would result in a 5n (pentaploid) hybrid. BO gametes would carry 2 sets of BO chromosomes, while Coastal BTK gametes would carry 3 sets of BTK chromosomes. The resultant hybrid would have 5 sets of chromosomes (5n = 30). Since the hybrid is an odd polyploid, one of the BTK sets has no homologous set to pair up with during synapsis:

Of course, the above explanation depends on a base number of 6. Based on my own count, Coastal BTK must be higher than 30. I suppose the sporophyte number could be 42, but then Coastal BTK itself will be a sterile odd polyploid. With 7 sets of chromosomes, one set will not have a homologous set to pair up with during synapsis. If Coastal BTK is 8n, then hybrids with BO and BT would be 6n and potentially fertile.

With base numbers of 6 and 8 chromosomes, most species of Brodiaea are technically polyploids with multiple sets of chromosomes. For example, B. terrestris ssp. kernensis in Kern County is an octoploid with eight sets of chromosomes, and B. orcuttii is tetraploid with four sets of chromosomes. [B. jolonensis in Monterey County is diploid with two sets of chromosomes.] According to Niehaus (1971), the lack of quadrivalents in meiosis plus the differences in size of individual mitotic chromosomes at different ploidy levels suggests that these are "old polyploids." That is, the tetraploids, hexaploids, and octoploids have been in existence long enough to change by translocations, deletions, and so on. These differences apparently are enough to ensure that during meiosis only bivalents will occur in the higher ploidy levels. In bivalents, only two sets of maternal and paternal chromosomes associate during synapsis of meiosis, in contrast to quadrivalent where four sets of homologous chromosomes associate during meiosis.

If Brodiaea species behave as diploids, then BF and BO each have n = 12 and 2n = 24, and BTK has n = 18 or a higher number. In fact, BTK could be 2n = 36, 38, 40, 42, 44, 46, 48, etc. and still be theoretically fertile with two sets of homologous chromosomes. A hybrid between BF or BO and BTK would be sterile because of the non-homologous pairs of chromosomes that differ in number. Hybridization may occur, but the resulting hybrid offspring grown from seed may by sterile without viable pollen. For example, a cross between BF and BTK could result in a hybrid with 12 BF chromosomes and 18 BTK chromosomes which would not match up during synapsis of prophase I. This hypothesis is a plausible explanation for the sterile hybrids we have observed in San Marcos.

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Natural interspecific hybridization in oaks (Quercus): A. California Black Oak (Q. kelloggii), a tall, deciduous tree; B. Gander Oak (Q. x ganderi), a partly deciduous tree that retains numerous leaves during the winter months; C. Coast Live Oak (Q. agrifolia), a large evergreen tree. The leaves of Q. x ganderi (B) have the intermediate size and lobes of Q. kelloggii), and the cup-like shape (upside-down cup) and pubescent (fuzzy), light green underside like Q. agrifolia. All three species occur in the mountains of San Diego County, although the hybrid (Q. x ganderi) is extremely rare.

See More Photos Of Oaks In San Diego County

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17. Hybrid Pines In San Diego County

Natural interspecific hybridization in pines (Pinus): A. Coulter Pine (Pinus coulteri), with large seed cones composed of thick, hooklike scales; B. Coulter-Jeffrey Hybrid, with intermediate-sized cones composed of thick scales without conspicuous hooks; C. Jeffrey Pine (P. jeffreyi), with slightly smaller cones bearing scales with slender, downwardly-pointed prickles. In general growth aspect the Coulter-Jeffrey hybrid (B) resembles a Jeffrey pine. The bark even has the faint vanilla odor typical of Jeffrey pines.

The fragrance of Jeffrey pine bark is caused by aromatic aldehydes in the oleoresin. The fragrant aldehydes and alkanes (n-heptane) of Jeffrey pine oleoresins are absent in the turpentines of the closely-related ponderosa pine (P. ponderosa). On a warm day, when the bark is heated by the sun, the fragrant aldehydes are unmistakable. The seed cones of the hybrid are clearly intermediate between the parental species. The scales are thick and heavy as in the Coulter pine, but do not have the conspicuous hooks. The scales terminate in stout, outwardly-pointed (slightly hooked) prickles, unlike the slender, downwardly-pointed prickles of Jeffrey pine. In color, the hybrid cones are intermediate between the yellowish-brown cones of Coulter pine and the darker, reddish-brown cones of Jeffrey pine. Some hybrid cones show a closer resemblance to one or the other parent, probably due to backcrossing between the hybrid and one of the original parents.

The Coulter pine is actually more closely related to the Torrey Pine (P. torreyana) and digger pine (P. sabiniana) of coastal and central California. In fact, the latter three species are placed in the Group Macrocarpae, characterized by distinctive, large, heavy seed cones with thick cone scales and large seeds. The Jeffrey pine belongs to the Group Australes, along with the ponderosa pine and several other New World species. What is interesting about the Coulter-Jeffrey hybrid is that the parental trees belong to different genetic groups within the genus Pinus in which cross pollination between groups is uncommon. Coulter-Jeffrey hybrids are rare, but can be found occasionally in the Laguna Mountains of San Diego County. Because of the combined genetic traits of hybrid trees (called hybrid vigor), Coulter-Jeffrey hybrids are being planted and tested for resistance to drought and dwarf mistletoe (Arceuthobium campylopodum) in San Diego County.

References Armstrong, W.P. 1978. "Four Wildflowers Vanishing From Northern San Diego County." Environment Southwest Number 480: 3-6. Armstrong, W.P. 1977. "Natural Plant Hybrids in San Diego County." Environment Southwest Number 477: 14-16. Mirov, N.T. 1967. The Genus Pinus. Ronald Press Company, New York.

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