All vegetation and plants that grew during Shemitah are Rabbinically forbidden to be eaten. This prohibition is called Sefichin. The prohibition includes any vegetation or grains that grew, even from seeds that fell the previous year, and certainly towards vegetation that was planted intentionally.
Fruits of a tree: Fruits of the tree are not forbidden due to Sefichin. Hence the only products that are permitted to be eaten if they grew during Shemitah are fruits of trees, as well as the exceptions to be mentioned below.
Not planted by majority of people: All plants that are not sowed in the ground by majority of people are not included in the prohibition of Sefichin and are hence permitted to be eaten.
Vegetables that grow yearly from the same root: Those vegetables that grow every single year from their same root, such as artichoke and pineapple, are not considered Sefichin if they began growing in the 6th year. If however they began growing in the Shemitah year they are forbidden due to Sefichin.
Vegetables that were picked during Shemitah: Some Poskim rule that vegetables that grew in the 6th year but were picked in the Shemitah year are forbidden due to Sefichin. Other Poskim rule it is not considered Sefichin and is hence permitted to be eaten as Kedushas Sheviis produce. Practically the custom follows the latter opinion.
Grains that started to grow before Shemitah and reached 1/3 during Shemitah: If the grain grew during Shemitah they are considered Sefichin as stated above. One follows the first 1/3 of the growth of the grain or legumes regarding its Shemitah status. Thus if it reached 1/3 of its growth in the 6th year then the grains and legumes do not contain Kedushas Sheviis. However if they reached 1/3 of their growth in the seventh year then it has a Kedushas Sheviis status and the produce must be disowned from the field. Some Poskim however rule that if they reached 1/3 of their growth in the 7th year then they are considered Sefichin.
In the 8th year: All Sefichin that grew in the Shemitah year are forbidden to be eaten even in the 8th year. Unless known otherwise, all vegetation and plantation of the 8th year is to be considered Sefichin until Chanukah. If one knows the product grew during Shemitah then it is forbidden even after Chanukah, unless that species has already been planted and grown in the 8th year.
Areas in Eretz Yisrael that were not conquered by the Babylonian exile: Do not contain the prohibition of Sefichin.
Land of a gentile: Vegetables that were planted and grew in the field of a gentile do not contain a prohibition of Sefichin. [Thus those that hold of Heter Mechirah allow eating vegetables grown in the field during Shemitah under this basis.]
Produce of ownerless property? The produce of ownerless land which is not cultivated is not included within the prohibition of Sefichin. Thus all land produce that grows in the wild is not considered Sefichin. [However if the land is cultivated then it contains the Sefichin prohibition even if it is ownerless land.]
Are flowers that grew during Shemitah considered Sefichin?
Some Poskim rule that flowers which are grown for their scent and have grown during Shemitah contain the Issur of Sefichin. Those flowers that are not grown for their scent do not contain an Issur of Sefichin. However some Poskim are stringent even by flowers that are not grown for their scent. Practically one may be lenient regarding flowers that are not grown for their scent. It however remains forbidden to plant any flowers during Shemitah according to all and purchasing such flowers may transgress the Issur of Nevad, Shamur and helping those that transgress.
Are bananas defined as Sefichin?
Are bush fruits and spices defined as Sefichin?
No as they grow from their roots each year.
Is rosemary that grew during Shemitah forbidden due to Sefichin?
No. However it contains Kedushas Sheviis starting from Cheshvan of Shemitah.
What is the status of Passiflora?
It remains unclear as to whether it has a status of a fruit or vegetable. Some write one may be lenient in this regard.
 Rambam 4/1-2; Toras Hashemitah 9/28
 The reason: The reason for this prohibition is due to a decree that people may come to plant during Shemitah and claim that the seeds grew on their own. Hence the Sages decreed to prohibit all vegetables that grew during Shemitah, even if they grew on their own. [Rambam 4/2]
 Rambam 4/3
 Rashas 5/3; See Sheves Haaretz 4/18
 See Peas Hashulchan
 Rabbeinu Shimshon
 Grach Naah p. 11; Peas Hashulchan;
 Grach Naah p. 11
 See Rambam 4/9 that we follow Onas Hamaasros
 Grach Naah ibid
 Sheves Haaretz p. 30; See Minchas Yerushalayim p. 104
 Toras Hashemitah 32
 See Chazon Ish 9/13; Sheves Haaretz 4/6
 Rambam 4/26
 Rambam 4/29
 The reason: As the gentiles are not commanded in Shemitah and hence the Sages never made the decree include their fields.
 Yalkut Yosef p. 34
 Based on Rambam 4/4 that the decree of Sefichin does not apply to a Sidei Bur.
 The reason: As people don’t generally grow produce on ownerless property and it is hence not included in the decree of Sefichin. [Rambam ibid]
 Chazon Ish 10/6
 Devar Shemitah; Minchas Yerushalayim 6/8
 Minchas Yerushalayim 6/9
 Brought in Minchas Yerushalayim 6/9
 Minchas Yerushalayim 6/9
 Grach Naah p. 66; Minchas Yitzchak 8/95 in name of Chazon Ish
 Minchas Yerushalayim 6/11
 The reason: As it is a bush that grows from year to year from the same root.