(1) The word "flower" is used for Ritu (season) also symbolically.
(2) Phool.  Pushp.  Kusum.
See the names of flowers on Next Page
Some flowers' names are given on this page with their pictures.

Flowers are used for many purposes, but two are main - (1) to decorate, and (2) for worship.

How and What Type of Flowers Should be Offered to Gods
(1) Flowers should always be offered to one's Deity fresh. Fresh means plucked on the same day. The use of dried out flowers or those infested with insects or wilted flowers are prohibited in the ritualistic worship of a Deity. There are two reasons for this according to spiritual science : Whatever we offer to a deity is accepted by the Deity on a subtle level and then they get pleased and bless us. Therefore whatever we offer to them has to be best. Secondly, the capacity of a flower is to absorb and emit the frequencies of Deity and Saatwik frequencies gets reduced if it is dry or infested with insects or wilted. The basic principle underlying offering flowers is that they are offered for their color, not for fragrance. As they become stale or wilted, they lose their color. Therefore one should always offer fresh flowers to a Deity on a daily basis after removing the old ones offered on the previous day.
(2) One should never use "used" flowers (Nirmaalya) to offer to Deity. Used flowers means - either they have been already offered to some Deity, or have been used for some other purposes.
(3) One should not offer a flower which has been touched to the body, have handled with left hand or have taken smell of it.
(4) We should not offer a flower which is without any fragrance, or has very strong fragrance, or has fallen on the ground, or has been kept on an unclean surface. In fact one should pluck flowers, should keep in a clean leaf, bring home and keep directly in the Poojaa Thaalee (plate) near the Deity. If one follows this practice, he is saved from all odds.
(5) A flower which is not bloomed up fully (buds or even half open flowers), or has its petals withered should not be offered.
(6) Stolen flowers should not to be offered. There is no harm in asking for flowers for Poojaa from somebody who has flowers abundantly, if you need many; otherwise if you need only a few, 4-6, even an owner of a few flowers can allow you to take them. People normally never refuse flowers for Poojaa, But one should be considerate enough that he should not ask flowers from the same person daily.
(7) The flowers which are wrapped in the leaves of Arka (rui or calatropis) or rend leaves should not be offered to a Deity.
(8) It is prohibited to offer flower dipped or washed in water, but one can always sprinkle them with water to keep them fresh.
(9) Do not pluck the flowers without taking bath
(10) Do not pluck flowers for Poojaa ritual with your shoes on.
(11) Express gratitude to the plant from which you are going to pluck the flowers.
(12) Pluck only that number of flowers as is necessary for the the Poojaa ritual. Chant of your favorite Deity while plucking the flowers.
(13) One should never pluck flowers after sunset. In fact one should never touch plants or sit under trees after sunset.

Why Not to Pluck Flowers After Sunset?
The life cycle of the living beings runs according to the cycle of nature. That is why everything has right time to be performed in our Hindu Samaatan Dharm; and for the same reason there is definite time for plucking of flowers also according to scriptures. So why not we pluck the buds or flowers after sunset? At Brahm Muhoort, 1 1/2 hours before sunrise, the Pavitrak of Deities are projected on a large scale on to the earth. These Pavitrak get attracted on a greater scale towards those flowers which have the capacity to attract Pavitrak of a particular Deity. The sunlight causes the disintegration of Rajo and Tamo Gunee particles present in the atmosphere. Therefore the atmosphere before the Sunset is more Saatwik as compared to that after the sunset.

However there are some exceptions to this rule. For example there are some flowers whose buds start opening at the sunset itself like those of Belaa, Chamelee (jasmine) and Rajaneegandhaa etc. These buds eagerly wait for the Brahm Muhoort. These flowers have more fragrance when compared to other flowers. That is why the Deity principles get attracted towards these flowers in large amount.

Another Note
If one does not have to offer any special flower to his Deity, one can grow a few plants of Sadaabahaar flowers (which bloom all over the year) in one's house and use those flowers for Poojaa. Since they come in many colors, one can grow whatever color he needs.

Which Flower to Which Deity?
Specific kinds of flowers are offered to specific Devtaa, such as

Durgaa - Either 1 or 9 Chamelee (jasmine) flowers
Ganapati - Red flowers, especially Gudahal (hibiscus) is offered to him
Hanumaan - 5 Chamelee (jasmine) flowers
Krishn - 3 Krishn Kamal flowers
Raam - 4 Jaya flowers
Saraswatee - She loves white color - Belaa, Chamelee,
Shiv - Bel Patra, Bel fruit are offered to him, white Dhatooraa flower. 10 Rajaneegandhaa flowers.
Soorya - Red colored flowers are offered to him - red Kaner
Vishnu - Manjaree or Tulasee flowers are offered to Him

Panch Flower Baan of Kaam Dev
There are Panch Pushp Baan (five flower arrows) of Manmath (Kaam Dev) - the five flowers are:
(1) Aravind   (2)  Ashok  flower (3) Mango flower  (4) Nava-Mallikaa - Chamelee  (5)  Neelotpal - Neel Kamal or Blue Lotus or blue Water Lily
and each of them is supposed to evoke a distinct aspect that characterizes the love-lorn.