The Company has two equity incentive plans: the 2006 Stock Plan (“2006 Plan”) and the 2015 Omnibus Equity Incentive Plan (“2015 Plan”).

In 2006, the Company adopted the 2006 Plan, which provided for the granting of stock options to executives, employees, and other service providers under terms and provisions established by the Board of Directors. The Company granted non-statutory stock options (“NSOs”) under the 2006 Plan until May 2015, when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding and were issued under the 2006 Plan. The 2015 Plan became effective upon the Company’s IPO in May 2015 and all shares that were reserved, but not issued, under the 2006 Plan were assumed by the 2015 Plan. Upon effectiveness, the 2015 Plan had 154,387 shares of common stock reserved for future issuance, which included 10,637 that were transferred to and assumed by the 2015 Plan. The 2015 Plan provides for automatic annual increases in shares available for grant. In addition, shares subject to awards under the 2006 Plan that are forfeited or canceled will be added to the 2015 Plan. The 2015 Plan provides for the grant of incentive stock options (“ISOs”), NSOs, restricted stock awards, stock units, stock appreciation rights, and other forms of equity compensation, all of which may be granted to employees, officers, non-employee directors, and consultants. The ISOs and NSOs will be granted at a price per share not less than the fair value at the date of grant. Options granted generally vest over a four-year period; however, the options granted in the third quarter of 2018 vest over two-year period, vesting monthly on a pro-rated basis. Options granted, once vested, are generally exercisable for up to 10 years, after grant.

In June 2019, the shareholders approved an amendment to the Company’s 2015 Plan for a one-time increase to the number of shares of common stock that may be issued under the 2015 Plan by 120,000 shares. As of December 31, 2020, a total of 1,047,243 shares of common stock were reserved for issuance under the 2015 Plan, of which 157,484 shares of common stock are available for future grant. As of December 31, 2020, a total of 19,172 and 870,587 options are outstanding under the 2006 and 2015 Plans, respectively. As of December 31, 2019, a total of 45,229 and 616,472 options are outstanding under the 2006 and 2015 Plans, respectively.

The following is a summary of stock option information and weighted average exercise prices under the Company’s stock incentive plans (in thousands, except share data and price per share):

	Shares Subject to Outstanding Options			Weighted- Average Exercise Price Per Share		Aggregate Intrinsic Value
Outstanding — Balance at December 31, 2018		530,044		$	35.53	$	—
Options granted		208,571			5.13
Options exercised		(546	)		4.63
Options forfeited		(30,132	)		33.95
Options expired		(46,236	)		98.69
Outstanding — Balance at December 31, 2019		661,701			21.60	$	305
Options granted		502,494			4.28
Options exercised		—			—
Options forfeited		(174,508	)		5.91
Options expired		(99,928	)		25.56
Outstanding — Balance at December 31, 2020		889,759			14.46	$	240
Vested and expected to vest — December 31, 2020		841,991			15.03	$	240
Exercisable —December 31, 2020		502,973		$	22.20	$	—

Aggregate intrinsic value represents the difference between the exercise price of the options and the estimated fair value of the Company’s common stock determined by our Board of Directors for each of the respective periods. The intrinsic value of options exercised was $0 for both years ended December 31, 2020 and 2019.

As of December 31, 2020, there was $0.7 million of unrecognized compensation cost related to unvested stock-based compensation grants that will be recognized over the weighted-average remaining recognition period of 2.77 years.

On August 22, 2019, Rajendra Ketkar provided notice to the Company of his retirement as Arcadia’s president, chief executive officer and director, effective as of September 1, 2019. On August 23, 2019, Arcadia and Mr. Ketkar entered into a Separation and Release Agreement (the “Separation Agreement”) which provides that the vesting of certain options previously issued to Mr. Ketkar will be accelerated pursuant to the terms of the Separation Agreement. In addition, the Separation Agreement extends the post-termination exercise period of the accelerated options from 90 days to up to two years. The stock compensation expense related to the modification of Mr. Ketkar’s stock options was $438,000 and recognized in selling, general and administrative expenses during the year ended December 31, 2019.

In determining the fair value of the stock-based awards, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment to determine.

Expected Term—The expected term is the estimated period of time outstanding for stock options granted and was estimated based on a simplified method allowed by the SEC due to insufficient historical data, and defines the term as the average of the contractual term of the options and the weighted-average vesting period for all open employee awards.

Expected Volatility—Since the Company was privately held and does not have a long trading history for its common stock, the expected volatility was estimated based on the average volatility for comparable publicly traded biotechnology companies over a period equal to the expected term of the stock option grants. When selecting comparable publicly traded biotechnology companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected life of the stock-based awards. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available.

Risk-Free Interest Rate—The risk-free interest rate is based on the interest rate of U.S. Treasuries of comparable maturities on the date the options were granted.

Expected Dividend—The expected dividend yield is based on the Company’s expectation of future dividend payouts to common stockholders.

The fair value of stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumption:

	Year Ended December 31,
Assumptions	2020		2019
Expected term (years)		6.48		7.04
Expected volatility	134%		99%
Risk-free interest rate	1.01%		2.01%
Expected dividend yield		—		—

The weighted- average, estimated grant date fair value of employee stock options granted during the years ended December 31, 2020 and 2019 was $3.80 and $5.13, respectively. The Company recognized $2.0 million and $2.3 million of compensation expense for stock options awards for the years ended December 31, 2020 and 2019, respectively.

The Company’s 2015 Employee Stock Purchase Plan (“ESPP”) became effective on May 14, 2015. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount of up to 15% of their eligible compensation through payroll deductions, subject to any plan limitations. After the first offering period, which began on May 14, 2015 and ended on February 1, 2016, the ESPP provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last day of the offering period. As of December 31, 2020, the number of shares of common stock reserved for future issuance under the ESPP is 105,036. The ESPP provides for automatic annual increases in the shares available for purchase beginning on January 1, 2016. As of December 31, 2020, 35,056 shares had been issued under the ESPP. The Company recorded $47,000 and $16,000 of ESPP related compensation expense for the years ended December 31, 2020 and 2019, respectively.