Palm Seed Germination1
Alan W. Meerow2
Palms are unique among woody ornamental plants because, with relatively few exceptions, palm species can only be propagated from seed. Palms are also notorious in the nursery trade for slow and uneven seed germination. It has been estimated that over 25% of all palm species require over 100 days to germinate and have less than 20% total germination (Tomlinson, 1990). The reasons for this remain obscure, as very little investigative work has been accomplished on seed dormancy conditions in palms. Nonetheless, the palm grower can maximize success with germinating palm seeds by paying careful attention to a number of basic guidelines. The purpose of this publication is to outline and discuss the various aspects of handling and germinating palm seeds in the most cost-effective and reliable manner possible.
The Palm Seed
Palm seeds vary tremendously with respect to size. Many palms have seeds no larger than 1/4 inch in diameter, while the largest seed of any flowering plant in the world is that of a palm (the double coconut, Lodoicea maldivica). The bulk of a palm seed is taken up by nutritive tissue called endosperm that provides food for the germinating seedling for a longer period of time than most flowering plants (Figure 1). The “milk” and white meat of a coconut are liquid and solid endosperm, respectively. The palm embryo is very small, either cylindrical or top-shaped. The seeds themselves may be either round or variously elongated. Their surfaces may be smooth or intricately sculptured. Some are surrounded by a hard, water- and air-impermeable coat. Fibers from the fruit wall frequently remain attached to the seed, even after cleaning.
Figure 1. Longitudinal and cross section through a coconut fruit.
Types of Palm Seed Germination
The way palm seeds germinate falls into one of two categories. In palms with remote germination (Figure 2a-c), the seedling axis develops at some distance from the actual seed. The first structure to emerge from the seed is called the “cotyledonary petiole.” It resembles, and many people mistake it for, the first seedling root. The cotyledonary petiole grows downward into the soil (sometimes very deeply) and swells at its base. From this swelling emerges the first seedling root (radicle) and seedling shoot (plumule). The actual cotyledon or seed leaf remains inside the seed, functioning as an absorptive organ called the “haustorium.” The haustorium transfers nutrients from the endosperm to the young seedling. In palm seeds with remote germination, the radicle persists for some time and produces lateral roots. The seeds of Mediterranean fan palms (Chamaerops humilis), Chinese fan palms (Livistona chinensis), date palms (Phoenix spp.) and Mexican fan palms (Washingtonia robusta) have remote germination.
The other main class of palm seed germination is called adjacent germination (Figure 2d-f). In these seeds, only a small portion of the cotyledon emerges from the seed. It appears as a swollen body abutting the seed surface and is called the “button.” The radicle and plumule emerge from the bottom and top of the button. In palms with adjacent germination, the first seedling root or radicle is usually narrow and very short lived and is quickly replaced by roots formed at the seedling stem base (adventitious roots). As with remote germination, a haustorium remains inside the seed absorbing food from the endosperm. Some common palms with adjacent germination include areca (Dypsis lutescens), King Alexander palm (Archontophoenix alexandrae) and coconut (Cocos nucifera). In coconut, however, the first stages of germination occur in the fibrous fruit wall that adheres to the seed. They cannot be observed without dehusking the nut.
A number of palm species (Bismarckia, for example) bury the seedling axis deep in the soil. These species require some special handling that will be discussed later in this circular.
Figure 2. Main classes of palm seed germination. A-B. Remote germination, date palm (Phoenix dactylifera). A. Early germination with cotyledonary petiole emerged and seedling root (radicle) beginning growth. B. Seedling stem (plumule) emerging from cotyledonary sheath. C. First leaf (eophyll) emerged, radicle continuing to elongate, and haustorium inside seed absorbing nutrients from endosperm. D-F. Adjacent germination, piccabean palm (Archontophoenix cunninghamiana). D. Early germination with button emerged. E. Seedling root (radicle) and stem (plumule) emerging from button. F. First leaves (eophylls) emerging, first adventitious root formed and supplanting radicle, and haustorium inside seed absorbing nutrients from endosperm.
Sources of Seed
Seeds may be collected from local sources (trees in the landscape) or purchased from commercial dealers. Local collection has certain advantages; the freshness, degree of maturity and parentage of the seed is usually known by the collector. If the seed will be s
November 8th, 2009 at 12:52 pm
Palm Seed Germination1
Alan W. Meerow2
Palms are unique among woody ornamental plants because, with relatively few exceptions, palm species can only be propagated from seed. Palms are also notorious in the nursery trade for slow and uneven seed germination. It has been estimated that over 25% of all palm species require over 100 days to germinate and have less than 20% total germination (Tomlinson, 1990). The reasons for this remain obscure, as very little investigative work has been accomplished on seed dormancy conditions in palms. Nonetheless, the palm grower can maximize success with germinating palm seeds by paying careful attention to a number of basic guidelines. The purpose of this publication is to outline and discuss the various aspects of handling and germinating palm seeds in the most cost-effective and reliable manner possible.
The Palm Seed
Palm seeds vary tremendously with respect to size. Many palms have seeds no larger than 1/4 inch in diameter, while the largest seed of any flowering plant in the world is that of a palm (the double coconut, Lodoicea maldivica). The bulk of a palm seed is taken up by nutritive tissue called endosperm that provides food for the germinating seedling for a longer period of time than most flowering plants (Figure 1). The “milk” and white meat of a coconut are liquid and solid endosperm, respectively. The palm embryo is very small, either cylindrical or top-shaped. The seeds themselves may be either round or variously elongated. Their surfaces may be smooth or intricately sculptured. Some are surrounded by a hard, water- and air-impermeable coat. Fibers from the fruit wall frequently remain attached to the seed, even after cleaning.
Figure 1. Longitudinal and cross section through a coconut fruit.
Types of Palm Seed Germination
The way palm seeds germinate falls into one of two categories. In palms with remote germination (Figure 2a-c), the seedling axis develops at some distance from the actual seed. The first structure to emerge from the seed is called the “cotyledonary petiole.” It resembles, and many people mistake it for, the first seedling root. The cotyledonary petiole grows downward into the soil (sometimes very deeply) and swells at its base. From this swelling emerges the first seedling root (radicle) and seedling shoot (plumule). The actual cotyledon or seed leaf remains inside the seed, functioning as an absorptive organ called the “haustorium.” The haustorium transfers nutrients from the endosperm to the young seedling. In palm seeds with remote germination, the radicle persists for some time and produces lateral roots. The seeds of Mediterranean fan palms (Chamaerops humilis), Chinese fan palms (Livistona chinensis), date palms (Phoenix spp.) and Mexican fan palms (Washingtonia robusta) have remote germination.
The other main class of palm seed germination is called adjacent germination (Figure 2d-f). In these seeds, only a small portion of the cotyledon emerges from the seed. It appears as a swollen body abutting the seed surface and is called the “button.” The radicle and plumule emerge from the bottom and top of the button. In palms with adjacent germination, the first seedling root or radicle is usually narrow and very short lived and is quickly replaced by roots formed at the seedling stem base (adventitious roots). As with remote germination, a haustorium remains inside the seed absorbing food from the endosperm. Some common palms with adjacent germination include areca (Dypsis lutescens), King Alexander palm (Archontophoenix alexandrae) and coconut (Cocos nucifera). In coconut, however, the first stages of germination occur in the fibrous fruit wall that adheres to the seed. They cannot be observed without dehusking the nut.
A number of palm species (Bismarckia, for example) bury the seedling axis deep in the soil. These species require some special handling that will be discussed later in this circular.
Figure 2. Main classes of palm seed germination. A-B. Remote germination, date palm (Phoenix dactylifera). A. Early germination with cotyledonary petiole emerged and seedling root (radicle) beginning growth. B. Seedling stem (plumule) emerging from cotyledonary sheath. C. First leaf (eophyll) emerged, radicle continuing to elongate, and haustorium inside seed absorbing nutrients from endosperm. D-F. Adjacent germination, piccabean palm (Archontophoenix cunninghamiana). D. Early germination with button emerged. E. Seedling root (radicle) and stem (plumule) emerging from button. F. First leaves (eophylls) emerging, first adventitious root formed and supplanting radicle, and haustorium inside seed absorbing nutrients from endosperm.
Sources of Seed
Seeds may be collected from local sources (trees in the landscape) or purchased from commercial dealers. Local collection has certain advantages; the freshness, degree of maturity and parentage of the seed is usually known by the collector. If the seed will be s